Don't share WorldMapCollection. Fixes BUKKIT-4871

WorldMapCollection stores scoreboard, map (item), structure, and
village information. Scoreboards are explicitly handled globally,
while villages and structures are erroneously shared.

This commit separates the WorldMapCollections to not be shared among
custom worlds. Maps are special-cased to maintain the previous shared
behavior.

src/main/java/net/minecraft/server/ItemWorldMap.java

@@ -14,7 +14,7 @@ public class ItemWorldMap extends ItemWorldMapBase {
 
     public WorldMap getSavedMap(ItemStack itemstack, World world) {
         String s = "map_" + itemstack.getData();
-        WorldMap worldmap = (WorldMap) world.a(WorldMap.class, s);
+        WorldMap worldmap = (WorldMap) world.getServer().getServer().worlds.get(0).a(WorldMap.class, s); // CraftBukkit - use primary world for maps
 
         if (worldmap == null && !world.isStatic) {
             itemstack.setData(world.b("map"));

src/main/java/org/bukkit/craftbukkit/CraftServer.java

@@ -730,7 +730,6 @@ public final class CraftServer implements Server {
             return null;
         }
 
-        internal.worldMaps = console.worlds.get(0).worldMaps;
         internal.scoreboard = getScoreboardManager().getMainScoreboard().getHandle();
 
         internal.tracker = new EntityTracker(internal);