- follow up patch to previous test which removed rpl_ddl.test
 - also remove the corresponding rpl_ndb_ddl.test which sources the
   same include file as the now removed test.
 - also remove the common test include file extra/rpl_tests/rpl_ddl.test
 - also remove disabling of rpl_ndb_ddl.test referencing bug
 - also remove mention of things which "should be merged to
   rpl_ddl.test" from rpl_innodb.test

(cherry picked from commit 18e4bf4ba7de29c228c7784b2a61bd47bdc61f75)