Fixed a potential crash (#3439)

* Fixes #3413 and fixes #3437.
* Removed extra dynamic storage clearings.
Thanks to @ecdarreola and @mazvi!

src/map/map.cpp

@@ -2760,10 +2760,7 @@ int map_delinstancemap(int m)
 	aFree(mapdata->block);
 	aFree(mapdata->block_mob);
 	map_free_questinfo(m);
-	mapdata->flag.clear();
-	mapdata->drop_list.clear();
 	mapdata->damage_adjust = {};
-	mapdata->skill_damage.clear();
 
 	mapindex_removemap( mapdata->index );
 	map_removemapdb(mapdata);