Bug 29625: Fix var name in Koha::BiblioUtils get_all_biblios_iterator

Bug 29625: Fix var name in Koha::BiblioUtils get_all_biblios_iterator

In Koha::BiblioUtils, get_all_biblios_iterator method is a class level method like get_from_biblionumber.
So its first arg should be named $class instead of $self.
Even if this var in not used.

Test plan :
1) Run Elasticsearch full rebuild with and without patch
2) Check all biblio records are in index

Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>