Refactor split migrator

LMS-2936

Removed a bunch of loc_mapper code
Cleaned up offering now being course and run in a few places
Removed extra db queries

Conflicts:
	common/lib/xmodule/xmodule/modulestore/tests/test_publish.py
Basically == to `as_published` but that only works on usage keys afaik. I noticed that the inheritance was still running b/c the revision was `draft`