oc-calendar: Use the calendar's time zone if it is present

If the event was created by the MAPI client, the client's time zone (if
present) is assigned to the event's calendar in iCalEvent+MAPIStore.
This way, we can use it to deliver the event's properties correctly.

OpenChange/MAPIStoreRecurrenceUtils.h

@@ -25,14 +25,10 @@
 
 #include <talloc.h>
 
-#import <Foundation/NSTimeZone.h>
-
 #import <NGCards/iCalCalendar.h>
 #import <NGCards/iCalRecurrenceRule.h>
 #import <NGCards/iCalTimeZone.h>
 
-@class NSTimeZone;
-
 @class iCalEvent;
 @class iCalRepeatableEntityObject;
 @class iCalRecurrenceRule;
@@ -55,7 +51,6 @@
 
 - (void) fillRecurrencePattern: (struct RecurrencePattern *) rp
                      withEvent: (iCalEvent *) event
-                    inTimeZone: (NSTimeZone *) timeZone
                       inMemCtx: (TALLOC_CTX *) memCtx;
 
 @end