[libc++][ranges] remove `__workaround_52970` (#85683)

## Abstract

This pull request removes the `__workaround_52970` concept. This concept
is a workaround for a bug described in #52970, which causes the compiler
to trigger ADL on a pointer to an incomplete type in an SFINAE context.
This bug is fixed in Clang 14.

## Reference

- [[clang] Don't typo-fix an expression in a SFINAE
context](https://reviews.llvm.org/D117603)
- [[libc++] [ranges] ADL-proof the [range.access]
CPOs.](https://reviews.llvm.org/D116239)