[clang][cli] Stop creating '-Wno-stdlibcxx-not-found' in cc1

This patch stops creating the '-Wno-stdlibcxx-not-found' argument in `CompilerInvocation::CreateFromArgs`.

The code was added in 2e7ab55e (a follow-up to D48297). However, D61963 removes relevant tests and starts explicitly passing '-Wno-stdlibcxx-not-found' to the driver. I think it's fair to assume this is a dead code.

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D97042