[clang-tools-extra] [clangd] Remove potential prefix from enum value names (PR #83412)

[Julian Schmidt via cfe-commits]

https://github.com/5chmidti commented:

When the enumerators start with the enum name, but the names contain a `_` as a separator, then applying this tweak will result in `_`-prefixed enumerators. Can you please handle that case as well and remove the `_`? Otherwise, this looks good to me

https://github.com/llvm/llvm-project/pull/83412