[hooks/syncschema] avoid altering a dropped table If the constraint's rdef is being removed, CWConstraintDelOp doesn't need to do anything. Otherwise it may try to alter a removed table/column. Closes #4154549

option_group_changed('port', 'main', 'web')
option_group_changed('query-log-file', 'main', 'web')
option_group_changed('profile', 'main', 'web')
option_group_changed('max-post-length', 'main', 'web')