[v2.4.x] Remove pins, use global pinning

[h-vetinari]

Follow-up to #322, let's see if we can move to the default pinning. There were some issues with fbgemm and clang 18 that look familiar, but where I don't remember how that was fixed. Perhaps @mgorny remembers or is interested.

[conda-forge-admin]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe/meta.yaml) and found it was in an excellent condition.

I do have some suggestions for making it better though...

For recipe/meta.yaml:

• ℹ️ The recipe is not parsable by parser conda-souschef (grayskull). This parser is not currently used by conda-forge, but may be in the future. We are collecting information to see which recipes are compatible with grayskull.
• ℹ️ The recipe is not parsable by parser conda-recipe-manager. The recipe can only be automatically migrated to the new v1 format if it is parseable by conda-recipe-manager.

_{This message was generated by GitHub Actions workflow run https://github.com/conda-forge/conda-forge-webservices/actions/runs/12866519409. Examine the logs at this URL for more detail.}

[h-vetinari]

OK, so clang 18 starts raising a -Wvla-cxx-extension warning in

  [412/7524] Building CXX object third_party/fbgemm/CMakeFiles/fbgemm_generic.dir/src/FbgemmI8Spmdm.cc.o
  FAILED: third_party/fbgemm/CMakeFiles/fbgemm_generic.dir/src/FbgemmI8Spmdm.cc.o
  $BUILD_PREFIX/bin/x86_64-apple-darwin13.4.0-clang++ -DFBGEMM_STATIC -I$SRC_DIR/third_party/cpuinfo/include -I$SRC_DIR/third_party/fbgemm/third_party/asmjit/src -I$SRC_DIR/third_party/fbgemm/include -I$SRC_DIR/third_party/fbgemm -isystem $SRC_DIR/third_party/XNNPACK/include -march=core2 -mtune=haswell -mssse3 -ftree-vectorize -fPIC -fstack-protector-strong -O2 -pipe -stdlib=libc++  -fmessage-length=0 -isystem $PREFIX/include -fdebug-prefix-map=$SRC_DIR=/usr/local/src/conda/libtorch-2.4.1 -fdebug-prefix-map=$PREFIX=/usr/local/src/conda-prefix -Wno-deprecated-declarations -Wno-unknown-warning-option -Wno-error=unused-command-line-argument -Wno-vla-cxx-extension -DTARGET_OS_OSX=1 -fvisibility-inlines-hidden -DUSE_PTHREADPOOL -fopenmp=libomp -Wall -Wextra -Werror -Wno-deprecated-declarations -Wimplicit-fallthrough -O3 -DNDEBUG -std=c++17 -isysroot /Applications/Xcode_15.2.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.3.sdk -mmacosx-version-min=10.15 -fPIC -fvisibility=hidden -MD -MT third_party/fbgemm/CMakeFiles/fbgemm_generic.dir/src/FbgemmI8Spmdm.cc.o -MF third_party/fbgemm/CMakeFiles/fbgemm_generic.dir/src/FbgemmI8Spmdm.cc.o.d -o third_party/fbgemm/CMakeFiles/fbgemm_generic.dir/src/FbgemmI8Spmdm.cc.o -c $SRC_DIR/third_party/fbgemm/src/FbgemmI8Spmdm.cc
  $SRC_DIR/third_party/fbgemm/src/FbgemmI8Spmdm.cc:86:32: error: variable length arrays in C++ are a Clang extension [-Werror,-Wvla-cxx-extension]
     86 |   alignas(64) uint8_t A_buffer[K * 32];
        |                                ^~~~~~

This then becomes a problem due to -Werror, and adding -Wno-vla-cxx-extension to CXXFLAGS doesn't change anything, presumably because the submodule doesn't respect ambient CXXFLAGS.

All things considered, this rabbit hole is not worth the effort ATM, so let's just stay on clang 17.