Bug 14066: Correct and optimize

Bug 14066: Correct and optimize

As far as I can tell $sunday is never used. And it seemed to be
scoped to only _init.

The remaining hashiness was cleaned up for the $return_by_hour.

TEST PLAN
---------
1) Apply both patches
2) (Skip this one - file does not exist / MV) prove -v t/db_dependent/Calendar.t
3) prove -v t/db_dependent/Holidays.t
4) prove -v t/Calendar.t
5) perlcritic -3 Koha/Calendar.pm
   -- the message corresponds to a comment in the code already
      and not this change.
6) run koha qa test tools

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>