Remove warning for custom entities in precreaturespawn, add note to event

We can't fix this. The event will simply not fire for hacky plugins replacing
entity registrations.

Spigot-API-Patches/PreCreatureSpawnEvent.patch

@@ -16,7 +16,7 @@ See: https://github.com/PaperMC/Paper/issues/917
 
 diff --git a/src/main/java/com/destroystokyo/paper/event/entity/PreCreatureSpawnEvent.java b/src/main/java/com/destroystokyo/paper/event/entity/PreCreatureSpawnEvent.java
 new file mode 100644
-index 00000000..c4751b61
+index 00000000..bac1cef3
 --- /dev/null
 +++ b/src/main/java/com/destroystokyo/paper/event/entity/PreCreatureSpawnEvent.java
 @@ -0,0 +0,0 @@
@@ -37,6 +37,7 @@ index 00000000..c4751b61
 + * The intent of this event is to improve server performance, so limited use cases.
 + * 
 + * Currently: NATURAL and SPAWNER based reasons. Please submit a Pull Request for future additions.
++ * Also, Plugins that replace Entity Registrations with their own custom entities might not fire this event.
 + */
 +public class PreCreatureSpawnEvent extends Event implements Cancellable {
 +    private final Location location;