LP#1971745 - speed up open-ils.storage.action.live_holds.wide_hash

LP#1971745 - speed up open-ils.storage.action.live_holds.wide_hash

Postgresql 10 and EG 3.9.0

The query to grab holds on the hold shelf was taking 35-50 seconds on
a test system to return 466 records.  Explain analyze showed that the
left join on asset.call_number was causing a sequential scan and reading
all asset.call_number rows.

Letting PG know that the two conditions of the join are mutually exclusive
seems to let PG know that an index scan is faster.

Signed-off-by: Josh Stompro <stomproj@larl.org>
Signed-off-by: Jason Stephenson <jstephenson@cwmars.org>