Revert "[clang] [unittest] Add a test for Generic_GCC::GCCVersion::Parse (#69078)"

This reverts commit b4b35a5.

That commit broke builds with -DBUILD_SHARED_LIBS=ON. The reason
is that clang::driver::toolchains::Generic_GCC::GCCVersion::Parse
isn't visible outside of the shared library, because
the Generic_GCC class is marked with LLVM_LIBRARY_VISIBILITY.

Author: mstorsjo

clang/unittests/Driver/CMakeLists.txt

@@ -9,7 +9,6 @@ set(LLVM_LINK_COMPONENTS
 add_clang_unittest(ClangDriverTests
   DistroTest.cpp
   DXCModeTest.cpp
-  GCCVersionTest.cpp
   ToolChainTest.cpp
   ModuleCacheTest.cpp
   MultilibBuilderTest.cpp