LP#1482757: Speed Up the Delete of Orphaned URIs in upgrade script

LP#1482757: Speed Up the Delete of Orphaned URIs in upgrade script

Modify the code that deletes orphaned asset.uri table entries in the
upgrade script to use IN logic on the subquery, because IN is much
faster than NOT IN.  Also take into account the link between
serial.item and asset.uri so that we don't accidentally delete URIs
used by serial items.

Signed-off-by: Jason Stephenson <jason@sigio.com>
Signed-off-by: Jessica Woolford <jwoolford@biblio.org>
Signed-off-by: Michele Morgan <mmorgan@noblenet.org>