In a Galera cluster it is not recommended to dml the MyISAM tables in the mysql schema. Therefore it is not possible to programatically drop triggers, stored procedures and functions by deleting it from the corresponding tables.
As a work-around, one can create a prepared statement to run the DDL. This works for ALTER TABLE statements. This way, from a stored procdure, one can programatically run alter tables.
Unfortunately, when using the same technique to drop a trigger, routine or function, this error appears:
Please implement this so we can do more DDL statements from stored procedures.