Bug 24175: Use itemnumber when searching for holds in SIP drop_hold

Bug 24175: Use itemnumber when searching for holds in SIP drop_hold

To test:
1 - place a hold for a patron
2 - Get SIP running
    https://wiki.koha-community.org/wiki/Koha_SIP2_server_setup
3 - edit the sip_cli_emulator.pl for hold_mode from '+' to '-'
4 - Attempt to cancel hold
5 - It fails
6 - Apply patch
7 - Try again
8 - It succeeds

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@helsinki.fi>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>