When doing a ALTER TABLE ... RENAME, MariaDB doesn't rename
original table to #sql-backup, which it does in other cases,
but insteads drops the original table directly. However
this optimization doesn't work in case of InnoDB table
with a foreign key constraint.

During copy algorithm, InnoDB fails to rename the foreign key
constraint(MDEV-25855). With this optimisation, InnoDB also
fails to drop the original table because the table has
FOREIGN Key constraint exist in INNODB_SYS_FOREIGN table.
This leads to orphan .ibd file in InnoDB dictionary.
so disabling this optimization when FK is involved.

Reviewer: monty@mariadb.org