[llvm] [STLExtras] Remove incorrect hack to make indexed_accessor_range operator== compatible with C++20 (PR #72220)

[Ilya Biryukov via llvm-commits]

ilya-biryukov wrote:

I am testing if our internal builds and the buildbot will break with this change. I have previously assumed they would break, but there were other patches flying around at the same time so maybe I had missed something. It'd be nice if we could land this change and it'd work with some released version of Clang and Clang at head.

I'll post the results of my investigation when I'm done.

https://github.com/llvm/llvm-project/pull/72220