Revert "[lld/mac] Port typo correction for undefined symbols from ELF port"

This caused crashes/assert failures for some Chromium developers, see comment
on the code review.

> Ports:
> - core feature: https://reviews.llvm.org/D67039
> - case mismatch: https://reviews.llvm.org/D70506
> - extern "C" suggestions: https://reviews.llvm.org/D69592,
>   https://reviews.llvm.org/D69650
>
> Does not port https://reviews.llvm.org/D71735 since I believe that that doesn't
> apply to lld/Mach-O.
>
> Differential Revision: https://reviews.llvm.org/D135038

This reverts commit 8c45e802.