Cleanup locally used variables in Calendar_hijri

Cleanup locally used variables in Calendar_hijri

* Some variables that were only used in the calendar_hijri.cxx
  are now moved out of the header file, and they are no loner
  member variables of the the class Calendar_hijri. They are now
  placed in the the i18npool namespace.
* Removed unused variables SynMonth, EveningPeriod and LeapYear
* Moved a global variable definition to the member function that was
  the only place it was used. It is now a local variable.

Change-Id: I8a8b25765bd8ed5640b1a0cfa46ec9903b460a53
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/125433
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
Tested-by: Jenkins