Fix .clang-tidy for clang-tidy 14 compatibility

Remove ExcludeHeaderFilterRegex and SystemHeaders options which are
not supported in clang-tidy 14 on Ubuntu 22.04.

- ExcludeHeaderFilterRegex was added in LLVM 15
- SystemHeaders is not a valid configuration key

The .clang-tidy file is now compatible with clang-tidy 14+. Note that
clang-tidy remains disabled in CI presets for build performance, but
can be re-enabled if desired.

Author: claude

.clang-tidy

@@ -13,5 +13,3 @@ Checks: >
 WarningsAsErrors: '*'
 # Check first-party (non-system, non-vendored) headers.
 HeaderFilterRegex: '.*'
-ExcludeHeaderFilterRegex: 'build/_deps/'
-SystemHeaders: false