[llvm] [X86]Remove X86-specific dead code in ScheduleDAGRRList.cpp (PR #67629)

[Shengchen Kan via llvm-commits]

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

LGTM for x86 part. I'm fine with the change if it does not affect other targets.

https://github.com/llvm/llvm-project/pull/67629