Arm backend: Fix VGF neural statistics test PAL init and dangling test target (#22136)

Two fixes for the VGF neural statistics tests added in #22074.

1. `VgfNeuralStatisticsTest.RuntimeConfigFallsBackToMode1` aborted.

The invalid-mode fallback path in
`get_vgf_neural_statistics_runtime_config()` calls `ET_LOG`, which
aborts with `ExecuTorch PAL must be initialized before call to
et_pal_current_ticks()` when the runtime has not been initialized.
Initialize the PAL in the test env fixture, the same way
`backends/arm/test/vela_external_blocks_test.cpp` does.

2. `//executorch/devtools/inspector/tests:vgf_neural_statistics_test`
failed to build.

The `python_unittest` target points at `vgf_neural_statistics_test.py`,
which was never added to the tree, so the target fails to build with
`File not found:
devtools/inspector/tests/vgf_neural_statistics_test.py`. Remove the
dangling target.



cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils
@Sebastian-Larsson @robell @rascani

Author: Gasoonjia

backends/arm/test/vgf_neural_statistics_test.cpp

@@ -12,6 +12,7 @@
 #include <vector>
 
 #include <executorch/backends/arm/runtime/VGFNeuralStatistics.h>
+#include <executorch/runtime/platform/runtime.h>
 
 namespace vgf = executorch::backends::vgf;
 
@@ -32,6 +33,9 @@ void set_env(const char* name, const char* value) {
 class ScopedNeuralStatisticsEnv {
  public:
   ScopedNeuralStatisticsEnv() {
+    // Reading the runtime config can ET_LOG, which aborts unless the PAL is up.
+    executorch::runtime::runtime_init();
+
     const char* enable = std::getenv(vgf::kVgfNeuralStatisticsEnableEnv);
     const char* mode = std::getenv(vgf::kVgfNeuralStatisticsModeEnv);
     if (enable != nullptr) {

devtools/inspector/tests/targets.bzl

@@ -27,14 +27,6 @@ def define_common_targets(is_fbcode = False):
         ],
     )
 
-    python_unittest(
-        name = "vgf_neural_statistics_test",
-        srcs = ["vgf_neural_statistics_test.py"],
-        deps = [
-            "//executorch/devtools/inspector:vgf_neural_statistics",
-        ],
-    )
-
     python_unittest(
         name = "event_blocks_test",
         srcs = ["event_blocks_test.py"],