[clang-tools-extra] [tool] Remove legacy argument `-ignore-insert-conflict` from `run-clang-tidy.py` (PR #127066)

[Piotr Zegar via cfe-commits]

PiotrZSL wrote:

> In version 14.0 looks like is not anymore:
Because, it were added in Clang 15.
Even now on main branch it's still utilized.




https://github.com/llvm/llvm-project/pull/127066