Do not call EntityRemoveEvent during worldgen (#12588)

Ports the follow commits from spigot to paper.
All credits to go the respective commit authors listed below.

CraftBukkit: 3b4fd5b321f4440a2b3a67f3945739b45e6e687f

By: md_5 <git@md-5.net>

paper-server/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java

@@ -1961,6 +1961,11 @@ public class CraftEventFactory {
             return;
         }
 
+        // SPIGOT-8041: Do not call event unless entity has been spawned into world
+        if (!entity.inWorld) {
+            return;
+        }
+
         Bukkit.getPluginManager().callEvent(new EntityRemoveEvent(entity.getBukkitEntity(), cause));
     }