Vector and BlockVector should use the same hashCode

For example, the getChunks method returns a Set<Vector2D> which is
actually comprised of BlockVector2D, so using set.contains(some vector)
will always return false.

There's unlikely to be multiple entities on the same block, or above
y=256, so using the int coords is better.

worldedit-core/src/main/java/com/sk89q/worldedit/BlockVector2D.java

@@ -80,12 +80,6 @@ public class BlockVector2D extends Vector2D {
 
     }
 
-    @Override
-    public int hashCode() {
-        return (Integer.valueOf((int) x).hashCode() >> 13) ^
-                Integer.valueOf((int) z).hashCode();
-    }
-
     @Override
     public BlockVector2D toBlockVector2D() {
         return this;