When dropping the util tables for upgrade, it's necessary to also drop
the events related to the table. This will enable new events to be
created which includes all columns of the table.

Make sure to add code to drop the extra event which may potentially
exist on mysql.ndb_schema due to legacy bug, although it was long ago
this is much clearer than the existing "allow_hardcoded_name" in
event_name_for_table(). Remove old workaround which is actually already
unreachable since the ndb_schema table can't be dropped any other way
than before upgrade.

Change-Id: Icd4376882a95be310ac3a95290baa71d5fc1cb49