[clang] [clang][RISCV] Remove `experimental` for vector crypto intrinsics (PR #106359)

[Brandon Wu via cfe-commits]

4vtomat wrote:

> Do we still need this?
> 
> ```
> def Experimental
>    : SubtargetFeature<"experimental", "HasExperimental",
>                       "true", "Experimental intrinsics">;
> ```

I guess we do in case there is any other extension that encounter the same situation lol~

https://github.com/llvm/llvm-project/pull/106359