[CMake] Remove BUILDING_WITH_TORCH_LIBS (#134434)

Since BUILDING_WITH_TORCH_LIBS is not used now.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/134434
Approved by: https://github.com/ezyang

CMakeLists.txt

@@ -490,10 +490,6 @@ if(USE_SYSTEM_LIBS)
   endif()
 endif()
 
-# Used when building Caffe2 through setup.py
-option(BUILDING_WITH_TORCH_LIBS
-       "Tell cmake if Caffe2 is being built alongside torch libs" ON)
-
 # /Z7 override option When generating debug symbols, CMake default to use the
 # flag /Zi. However, it is not compatible with sccache. So we rewrite it off.
 # But some users don't use sccache; this override is for them.

scripts/build_windows.bat

@@ -22,10 +22,6 @@ if NOT DEFINED BUILD_SHARED_LIBS (
   )
 )
 
-IF NOT DEFINED BUILDING_WITH_TORCH_LIBS (
-  set BUILDING_WITH_TORCH_LIBS=OFF
-)
-
 if NOT DEFINED CAFFE2_STATIC_LINK_CUDA (
   set CAFFE2_STATIC_LINK_CUDA=OFF
 )

tools/setup_helpers/cmake.py

@@ -204,7 +204,6 @@ class CMake:
                     "UBSAN_FLAGS",
                     "BLAS",
                     "WITH_BLAS",
-                    "BUILDING_WITH_TORCH_LIBS",
                     "CUDA_HOST_COMPILER",
                     "CUDA_NVCC_EXECUTABLE",
                     "CUDA_SEPARABLE_COMPILATION",