Revert "[Clang] Implement the 'counted_by' attribute (#76348)"

This reverts commit fefdef80.

Breaks check-clang, see
https://github.com/llvm/llvm-project/pull/76348#issuecomment-1886029515

Also revert follow-on "[Clang] Update 'counted_by' documentation"

This reverts commit 4a3fb9ce.