Bug 11799: Housekeeping: Remove _biblionumber_sth from VirtualShelves.pm

Bug 11799: Housekeeping: Remove _biblionumber_sth from VirtualShelves.pm

This routine is no longer used.

Test plan:
Do a grep on the name.
(Bonus points:) Verify if you can perform some actions on lists.

No more occurences of _biblionumber_sth found
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit 5e0d450875f24d1f9ef6620b033b5179633589da)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>