Revert "Make end tag singleton"

This reverts commit 13d2ae20
Why was this changed. I doubt it did much in terms of performance. It's better to stay as close as we can to the worldedit repo.

worldedit-forge/src/main/java/com/sk89q/worldedit/forge/NBTConverter.java

@@ -217,7 +217,7 @@ final class NBTConverter {
     }
 
     public static EndTag fromNative(NBTTagEnd other) {
-        return EndTag.INSTANCE;
+        return new EndTag();
     }
 
     public static LongTag fromNative(NBTTagLong other) {