[clang] [llvm] Remove experimental from Vector Crypto extensions (PR #69000)

[Brandon Wu via cfe-commits]

4vtomat wrote:

> Do we need to add the "experimental" feature to RISCVFeatures.td? If the feature string shows up in the function attributes, won't the backend print that it doesn't recognize the feature name when it parses the string?

Yes, we do, I forgot it lol~

https://github.com/llvm/llvm-project/pull/69000