Replace stubs with parent implementations.

Which makes real sense; reference from
https://github.com/inverse-inc/sogo/pull/201#discussion_r54880038 and
https://github.com/inverse-inc/sogo/pull/201#discussion_r54880094

SoObjects/Appointments/SOGoCalendarComponent.m

@@ -132,21 +132,12 @@
 
 - (void) setIsNew: (BOOL) newIsNew
 {
-  // Required for protocol <SOGoComponentOccurence>
-  // but not yet implemented.  Violently warn if
-  // used.
-  NSLog (@"SOGoCalendarComponent::setIsNew is not implemented.");
-  abort();
+  [super setIsNew: newIsNew];
 }
 
 - (BOOL) isNew
 {
-  // Required for protocol <SOGoComponentOccurence>
-  // but not yet implemented.  Violently warn if
-  // used.
-  NSLog (@"SOGoCalendarComponent::isNew is not implemented.");
-  abort();
-  return false;
+  return [super isNew];
 }
 
 - (NSException *) changeParticipationStatus: (NSString *) newPartStat