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

[Pengcheng Wang via cfe-commits]

https://github.com/wangpc-pp commented:

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

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