Remove no longer needed undead horse leash patch

This is now default vanilla behavior

Fixes #3644

Spigot-Server-Patches/0236-Implement-World.getEntity-UUID-API.patch

@@ -0,0 +1,26 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Brokkonaut <hannos17@gmx.de>
+Date: Tue, 3 Jul 2018 16:08:14 +0200
+Subject: [PATCH] Implement World.getEntity(UUID) API
+
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+index 89c8d3e6e6b7e1b1ac52aa2921e4dbf398ecb15a..5510281bef051280fb9495f21cade571d7547042 100644
+--- a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
++++ b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+@@ -1296,6 +1296,15 @@ public class CraftWorld implements World {
+         return list;
+     }
+ 
++    // Paper start - getEntity by UUID API
++    @Override
++    public Entity getEntity(UUID uuid) {
++        Validate.notNull(uuid, "UUID cannot be null");
++        net.minecraft.server.Entity entity = world.getEntity(uuid);
++        return entity == null ? null : entity.getBukkitEntity();
++    }
++    // Paper end
++
+     @Override
+     public void save() {
+         org.spigotmc.AsyncCatcher.catchOp("world save"); // Spigot