Re-Enable --delete functionality in umdl
Re-Enable --delete functionality in umdl

Since being ported to MM2 umdl's --delete functionality has never been
used and was still using the old and now not-existing SQLObject
interface. Change it to use the SQLAlchemy interface.

Running umdl with --delete decreases the size of the Fedora MM instance
database dump from 800MB to 760MB.

pombredanne/mirrormanager2,pombredanne/mirrormanager2,pombredanne/mirrormanager2,pombredanne/mirrormanager2