[llvm] workflows/release-binaries: Drop x86_64 Mac OS builds (PR #165645)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 approved this pull request.

Seems reasonable enough to me. x86 MacOS is becoming less important as time goes on.

https://github.com/llvm/llvm-project/pull/165645