Bug #33688509 row_drop_table_for_mysql assert for utf8mb3

We were getting an assert in InnoDB during data dictionary upgrade, if
the definition of the table 'innodb_ddl_log' had any changes.

The fix is to ignore changes that are in effect NO-OPs, such as
    utf8     <=> utf8mb3
    utf8_bin <=> utf8mb3_bin

Change-Id: I90f30890765e617b7e9edcc78a54e59ce90cb987

Author: Tor Didriksen