[clang] [llvm] [RISCV]Remove experimental from Zalasr (PR #177120)

[Sam Elliott via cfe-commits]

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

LGTM.

I'm not sure there have been any Zalsr changes since the 22.x branch. If this is the case, do we want to backport this?

https://github.com/llvm/llvm-project/pull/177120