Bug 36019: Remove dead code in tags/review

Bug 36019: Remove dead code in tags/review

Since bug 20489 it is no longer possible to login with the DB user.
At the time, get_template_and_user returned borrowernumber=0 in this case.

In tags/review.pl we have:
  $borrowernumber == 0 and push @errors, {op_zero=>1};

This condition is never met, and op_zero related code can be removed in the template.

Test plan:
Confirm the above

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>