[clang] [Tooling] Simplify a use of std::is_same (NFC) (PR #160237)

[Jakub Kuderski via cfe-commits]

kuhar wrote:

> > std::is_same<...>::type is the same as std::is_same<...>.
> 
> This is technically not true. `is_same<T, U>::type` names a specialization of `integral_constant`, not `is_same`.

I think the point is that it's the same for the purpose of SFINAE?

https://github.com/llvm/llvm-project/pull/160237