[clang][lex] NFC: Remove unused HeaderFileInfo member

This patch removes `HeaderFileInfo::isNonDefault`, which is not being used anywhere.

Reviewed By: dexonsmith, vsapsai

Differential Revision: https://reviews.llvm.org/D114092

GitOrigin-RevId: 7b6790850968031fe1c098ed6dcc196ddc547ea5
1 file changed