Bug 11337: Remove the C4::Serials::GetSubscriptions routine

Bug 11337: Remove the C4::Serials::GetSubscriptions routine

Since SearchSubscriptions is the way to search subscriptions, each call
to GetSubscriptions could be replaced by a call to SearchSubscriptions.

Test plan:
Verify following pages display the same thing as before this patch:
- catalogue/detail.pl
- opac/opac-ISBDdetail.pl
- opac/opac-detail.pl

Verify the following page returns correct results:
- serials/checkexpiration.pl

Verify the Serials UT file still passes:
- prove t/db_dependent/Serials.t

Note: The title filter on checkexpiration now only searches on the title
DB field. I don't think it is a regression, it should be the way to use
this field. Maybe should we add new search fields on this form.
Bug 5337 reintroduces a bug fixed by bug 5864, this patch restore the
right way to search subscription (based on biblionumber).

Signed-off-by: Aleisha <aleishaamohia@hotmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>