Suppress warning about prefixless date variable in calendar

Suppress warning about prefixless date variable in calendar

* lisp/calendar/lunar.el (date):
* lisp/calendar/cal-persia.el (date):
* lisp/calendar/cal-mayan.el (date):
* lisp/calendar/cal-julian.el (date):
* lisp/calendar/cal-iso.el (date):
* lisp/calendar/cal-islam.el (date):
* lisp/calendar/cal-hebrew.el (date):
* lisp/calendar/cal-french.el (date):
* lisp/calendar/cal-coptic.el (date):
* lisp/calendar/cal-china.el (date):
* lisp/calendar/cal-bahai.el (date): Suppress warning about this
prefix-less dynamic variable, because it's part of the documented
calling convention used in the sexp part of users' diary files.