This addresses the third aspect of Bug #41609.

row_mysql_drop_temp_tables(): New function, to drop all temporary
tables. These can be distinguished by the least significant bit of
MIX_LEN. However, we will skip ROW_FORMAT=REDUNDANT tables, because in
the records for those tables, that bit may be garbage.

recv_recovery_from_checkpoint_finish(): Invoke
row_mysql_drop_temp_tables().  Normally, if the .frm files for the
temporary tables exist at startup, MySQL will ask InnoDB to drop the
temporary tables.  However, if the files are deleted, for instance, by
the boot scripts of the operating system, the tables would remain in
the InnoDB data dictionary unless someone digs them up by
innodb_table_monitor and creates .frm files for dropping the tables.

rb://221 approved by Sunny Bains.