Remove support for experimental/custom cmake + visual studio. NFC (#20901)

This support was added in 2013 but never maintained or tested so I
assume it was never completed.  An additional motivation for removing
this is that it it should allow the removal of `--default-obj-ext`.

Author: sbc100

cmake/Modules/Platform/Emscripten.cmake

@@ -354,35 +354,6 @@ function(em_link_post_js target)
   em_add_link_deps(${target} "--post-js" ${ARGN})
 endfunction()
 
-# Experimental support for targeting generation of Visual Studio project files
-# (vs-tool) of Emscripten projects for Windows.  To use this, pass the
-# combination -G "Visual Studio 10" -DCMAKE_TOOLCHAIN_FILE=Emscripten.cmake
-if ("${CMAKE_GENERATOR}" MATCHES "^Visual Studio.*")
-  # By default, CMake generates VS project files with a
-  # <GenerateManifest>true</GenerateManifest> directive.
-  # This causes VS to attempt to invoke rc.exe during the build, which will fail
-  # since app manifests are meaningless for Emscripten.  To disable this, add
-  # the following linker flag. This flag will not go to emcc, since the Visual
-  # Studio CMake generator will swallow it.
-  set(EMSCRIPTEN_VS_LINKER_FLAGS "/MANIFEST:NO")
-  # CMake is hardcoded to write a ClCompile directive
-  # <ObjectFileName>$(IntDir)</ObjectFileName> in all VS project files it
-  # generates.  This makes VS pass emcc a -o param that points to a directory
-  # instead of a file, which causes emcc autogenerate the output filename.
-  # CMake is hardcoded to assume all object files have the suffix .obj, so
-  # adjust the emcc-autogenerated default suffix name to match.
-  set(EMSCRIPTEN_VS_LINKER_FLAGS "${EMSCRIPTEN_VS_LINKER_FLAGS} --default-obj-ext .obj")
-  # Also hint CMake that it should not hardcode <ObjectFileName> generation.
-  # Requires a custom CMake build for this to work (ignored on others)
-  # See http://www.cmake.org/Bug/view.php?id=14673 and https://github.com/juj/CMake
-  set(CMAKE_VS_NO_DEFAULT_OBJECTFILENAME 1)
-
-  # Apply and cache Emscripten Visual Studio IDE-specific linker flags.
-  set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${EMSCRIPTEN_VS_LINKER_FLAGS}" CACHE STRING "")
-  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} ${EMSCRIPTEN_VS_LINKER_FLAGS}" CACHE STRING "")
-  set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} ${EMSCRIPTEN_VS_LINKER_FLAGS}" CACHE STRING "")
-endif()
-
 if (NOT DEFINED CMAKE_CROSSCOMPILING_EMULATOR)
   find_program(NODE_JS_EXECUTABLE NAMES nodejs node)
   if(NODE_JS_EXECUTABLE)