Bug 24467: Remove _count methods introduced for API use

Bug 24467: Remove _count methods introduced for API use

This patch removes some methods that were introduced for API usage in
the first iteration of the object embedding development effort.

Those methods were obsoleted by bug 24528, which introduces a smarter
way for Koha::Object->to_api to embed *_count attributes on the output
structure based on the relationships and a call to ->count.

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/Biblio.t
=> SUCCESS: Tests pass
3. Sign off :-D

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>