API 29: Clean up unintentionally published checkNotUsed / markUsed

These methods were unintentionally published with the switch to metalava in 28, but
they were never really accessible to apps, because they are protected in a final class.

Bug: 123221743
Test: make api-stubs-docs-check-last-released-api
Change-Id: I88c3bbd2f68cf7c82d0ec5b2ef35edf1fad59004
1 file changed