Remove image delete tests from test_nodepool
Remove image delete tests from test_nodepool

Since nodepool scheduler doesn't deal with image deletes any more, we
we can remove them.

We now have coverage in test_dib_image_delete() that images are
actually deleted.

Change-Id: I4c7f622b72fedc438e9325dbf7a512bdd3c3b9d5
Signed-off-by: Paul Belanger <e7139c8e6c4ea75cc1c287ce081b2dc0f3ab39ec@redhat.com>

Tesora/tesora-nodepool,Tesora/tesora-nodepool