perf: Enable TBB parallelization unconditionally in HessianFactor

Remove conditional check for GTSAM_TBB_BOUNDED_MEMORY_GROWTH_FLAG to
always enable TBB parallelization when GTSAM_USE_TBB is defined.

Improves optimizer performance on my test case with
12 cores by ~27% (117.2s -> 85.7s) by reducing
iteration times from ~5-6s to ~3s.

before:
```
 ./build_RelWithDebInfo/simple_gtsam_deserialize
simple_gtsam_deserialize2.cpp
Reading values file took 0.0108 seconds
Reading graph file took 0.1702 seconds
Processing factor lines took 2.7537 seconds
Processing values lines took 0.1056 seconds
Setting up optimizer took 9.1390 seconds
Initial error: 83467.7055, values: 65796
iter      cost      cost_change    lambda  success iter_time
   0          inf         0.00       0.00      0       1.47
iter      cost      cost_change    lambda  success iter_time
   0     80421.88      3045.82       0.00      1       6.98
   1          inf         0.00       0.00      0       0.89
   1     80163.07       258.81       0.00      1       6.23
   2          inf         0.00       0.00      0       1.07
   2     80113.89        49.18       0.00      1       6.51
   3          inf         0.00       0.00      0       1.09
   3     80096.39        17.50       0.00      1       6.75
   4          inf         0.00       0.00      0       1.10
   4     80089.79         6.60       0.00      1       5.43
   5          inf         0.00       0.00      0       0.86
   5     80086.41         3.38       0.00      1       5.08
   6          inf         0.00       0.00      0       0.89
   6     80084.44         1.98       0.00      1       5.02
   7          inf         0.00       0.00      0       0.88
   7     80083.05         1.39       0.00      1       5.06
   8          inf         0.00       0.00      0       0.88
   8     80081.84         1.21       0.00      1       5.31
   9          inf         0.00       0.00      0       0.89
   9     80080.52         1.32       0.00      1       5.14
  10          inf         0.00       0.00      0       0.90
  10     80078.92         1.60       0.00      1       5.20
  11          inf         0.00       0.00      0       0.87
  11     80076.99         1.93       0.00      1       5.27
  12          inf         0.00       0.00      0       0.90
  12     80074.94         2.05       0.00      1       5.25
  13          inf         0.00       0.00      0       0.88
  13     80073.22         1.72       0.00      1       5.23
  14          inf         0.00       0.00      0       0.88
  14     80071.87         1.34       0.00      1       5.08
  15          inf         0.00       0.00      0       0.87
  15     80071.04         0.83       0.00      1       5.09
  16          inf         0.00       0.00      0       0.90
  16     80070.76         0.28       0.00      1       5.22
Running gtsam optimizer took 117.2392 seconds
```
After:
```
./build_RelWithDebInfo/simple_gtsam_deserialize
simple_gtsam_deserialize2.cpp
Reading values file took 0.0124 seconds
Reading graph file took 0.1912 seconds
Processing factor lines took 3.0148 seconds
Processing values lines took 0.1227 seconds
Setting up optimizer took 10.6574 seconds
Initial error: 83467.7055, values: 65796
iter      cost      cost_change    lambda  success iter_time
   0          inf         0.00       0.00      0       1.96
iter      cost      cost_change    lambda  success iter_time
   0     80421.88      3045.82       0.00      1       5.44
   1          inf         0.00       0.00      0       0.97
   1     80163.07       258.81       0.00      1       3.14
   2          inf         0.00       0.00      0       0.92
   2     80113.89        49.18       0.00      1       2.98
   3          inf         0.00       0.00      0       0.92
   3     80096.39        17.50       0.00      1       3.09
   4          inf         0.00       0.00      0       0.91
   4     80089.79         6.60       0.00      1       2.98
   5          inf         0.00       0.00      0       0.91
   5     80086.41         3.38       0.00      1       2.94
   6          inf         0.00       0.00      0       0.90
   6     80084.44         1.98       0.00      1       3.00
   7          inf         0.00       0.00      0       0.90
   7     80083.05         1.39       0.00      1       2.99
   8          inf         0.00       0.00      0       0.91
   8     80081.84         1.21       0.00      1       3.09
   9          inf         0.00       0.00      0       0.90
   9     80080.52         1.32       0.00      1       3.06
  10          inf         0.00       0.00      0       1.12
  10     80078.92         1.60       0.00      1       3.69
  11          inf         0.00       0.00      0       1.27
  11     80076.99         1.93       0.00      1       3.72
  12          inf         0.00       0.00      0       1.19
  12     80074.94         2.05       0.00      1       3.94
  13          inf         0.00       0.00      0       1.19
  13     80073.22         1.72       0.00      1       3.81
  14          inf         0.00       0.00      0       1.15
  14     80071.87         1.34       0.00      1       3.60
  15          inf         0.00       0.00      0       1.15
  15     80071.04         0.83       0.00      1       3.86
  16          inf         0.00       0.00      0       1.15
  16     80070.76         0.28       0.00      1       3.85
Running gtsam optimizer took 85.6852 seconds
```

Author: tzvist

gtsam/linear/HessianFactor.cpp

@@ -258,7 +258,7 @@ HessianFactor::HessianFactor(const GaussianFactorGraph& factors,
   // already running in parallel (e.g., when constructing multiple factors
   // concurrently), so there's no need to parallelize the inner
   // updateHessian loop here as well.
-#if defined(GTSAM_USE_TBB) && defined(GTSAM_TBB_BOUNDED_MEMORY_GROWTH_FLAG)
+#if defined(GTSAM_USE_TBB)
   constexpr DenseIndex kParallelThresholdHeuristic = 50;
   if (info_.rows() > kParallelThresholdHeuristic) {
     gttic(updateHessian_TBB);