Remove CLion's `.idea` folder that contains code style checks

[unterumarmung]

Clang-Tidy allows to specify code style settings in a config file, so .idea folder is redundant.

Official docs: https://clang.llvm.org/extra/clang-tidy/checks/readability-identifier-naming.html Example config: https://github.com/YACLib/YACLib/blob/main/.clang-tidy