Bug 21154: Remove unused subs from C4::Serials

Bug 21154: Remove unused subs from C4::Serials

Test plan:
Run these commands, grep should not return any occurences, prove should
return green:

git grep GetSerialStatusFromSerialId
git grep GetDistributedTo
git grep SetDistributedTo
git grep SetDistributedto
git grep in_array
git grep is_barcode_in_use

kshell
prove t/db_dependent/Serials.t

Signed-off-by: Pierre-Luc Lapointe <pierreluc.lapointe@inLibro.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>