[libc++][CMake] Removes LIBCXX_ENABLE_CLANG_TIDY. (#85794)

The clang-tidy selection in CMake was refactored in
https://github.com/llvm/llvm-project/pull/81362. During review it was
suggested to remove this CMake option.

GitOrigin-RevId: 6775285e7695f2d45cf455f5d31b2c9fa9362d3d
6 files changed