Remove no longer needed undead horse leash patch

This is now default vanilla behavior

Fixes #3644

Spigot-Server-Patches/Configurable-Non-Player-Arrow-Despawn-Rate.patch

@@ -10,8 +10,8 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 --- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
 +++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
 @@ -0,0 +0,0 @@ public class PaperWorldConfig {
-     private void allowLeashingUndeadHorse() {
-         allowLeashingUndeadHorse = getBoolean("allow-leashing-undead-horse", false);
+     private void nonPlayerEntitiesOnScoreboards() {
+         nonPlayerEntitiesOnScoreboards = getBoolean("allow-non-player-entities-on-scoreboards", false);
      }
 +
 +    public int nonPlayerArrowDespawnRate = -1;