Lp 1799272: Limit SIP2 hold items to available hold items.

Lp 1799272: Limit SIP2 hold items to available hold items.

Only inlcude holds that are available for pickup in the hold items
count and hold items fields of the SIP2 patron information
response. Given some confusion over the purpose of this field, that
there is also a field to list unavailable holds, and that a list of
holds avaialable for pickup would be more useful than a list of all
holds to a patron using a self-check, this seems like a good change.

Signed-off-by: Jason Stephenson <jason@sigio.com>