Make sure we don't try to use a deleted rev ID.

Make sure we don't try to use a deleted rev ID.

MySQL until 8.0 and MariaDB until some version after 10.1.34 don't save
the auto-increment value to disk, so on server restart it might reuse
IDs from deleted revisions. We can fix that with an insert with an
explicit rev_id value, if necessary.

Bug: T202032
Change-Id: I14e5b6c8ec8b5f1aeb2305fae4b103665f8f6686