World|DMU API|Sector: A sector's mobj list is no longer writable via DMU

Linking mobjs to mobj elements is the engine's job. There should be
no need for a game plugin to manipulate this list manually, so this
is now prevented at API level.

doomsday/client/src/world/sector.cpp

@@ -767,9 +767,9 @@ int Sector::property(DmuArgs &args) const
         SoundEmitter const *emitterAdr = &d->emitter;
         args.setValue(DMT_SECTOR_EMITTER, &emitterAdr, 0);
         break; }
-    case DMT_MOBJS:
+    /*case DMT_MOBJS:
         args.setValue(DMT_SECTOR_MOBJLIST, &d->mobjList, 0);
-        break;
+        break;*/
     case DMU_VALID_COUNT:
         args.setValue(DMT_SECTOR_VALIDCOUNT, &d->validCount, 0);
         break;