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

[Pengcheng Wang via llvm-commits]

wangpc-pp wrote:

> 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?

+1, I'd prefer to backport this as well. We haven't touched `Zalasr` part for a long time so I think it should be *safe*. :-)

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