Restore DROP QRTZ_JOB_LISTENERS and DROP QRTZ_TRIGGER_LISTENERS

While upgrading from v1.0-RC2, I was unable to run the tables_mysql.sql script without dropping QRTZ_JOB_LISTENERS and QRTZ_TRIGGER_LISTENERS.  It appears this used to happen, and would not hurt to have present.

https://github.com/grails-plugins/grails-quartz/blob/v1.0-RC2/src/templates/sql/tables_mysql.sql