Revert "Initial scheduler support for instance_groups"

This reverts commit b2c17ae891b12118b9d11bf0ecc44e77956715c8.

While reviewing merged changes, I came across this one.  It's using the
conductor in a way that it shouldn't.  The scheduler has db access, so
there's no need to add the extra conductor overhead.  The best thing to
do here is to just revert for now, IMO.

Change-Id: Iaa0d67df7bb84913784d925cffebcd5f252249ea
Merge "Revert "Initial scheduler support for instance_groups""