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

[Vicente Mataix Ferrándiz via cfe-commits]

loumalouomega wrote:

Ok, so is not legacy, but the contrary. My version of Clang is old. I can refactor if you want.

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