[clangd] Fix assertion crashes on unmatched NOLINTBEGIN comments.

The overload shouldSuppressDiagnostic seems unnecessary, and it is only
used in clangd.

This patch removes it and use the real one (suppression diagnostics are
discarded in clangd at the moment).

Fixes https://github.com/clangd/clangd/issues/929

Differential Revision: https://reviews.llvm.org/D113999

GitOrigin-RevId: 4ea066acc928d772c2a610024b7f0656b36e6afd
4 files changed