[clang] [clang][ci] Remove unnecessary BuildKite jobs for Clang (PR #93233)

[Vlad Serebrennikov via cfe-commits]

https://github.com/Endilll approved this pull request.

OK, I'll try to add this testing to "GitHub Pull Requests" later so that we can avoid building Clang twice.

https://github.com/llvm/llvm-project/pull/93233