not be dropped if the DEFINER is custom. Revert changes
to MDEV-23102 tests as they were designed to catch
this corner case.
The explanation for this corner case is that users
historically used to tweak the mysql.user table and
probably still do even though mysql.user is now a view.
Thus, if the DEFINER of the view is not default, i.e.
root@localhost or mariadb.sys@localhost, we should avoid
dropping the view during upgrade process to not discard
potential custom changes.