AUTO-419 - delete a group's events from the scaling schedule table (ready for review)

When deleting a group, also delete its entries in the scaling schedule table

This does not fix the update problem.

A couple problems with this:

1. That helper function for getting the delete events query and param is pretty hideous.  The `.rstrip` is also kind of meh.  Perhaps I should just add the semicolon to the other statement.  Not sure what else to do without a big-ish refactor.

2. This doesn't ensure that someone might go and create a scheduling policy right after the delete lists all policies, and so those events won't be deleted from the table.  But I think that might be ok?  The scheduler will eventually clean up those events.