Force compile-time failures for the subtle changes done in the API

By: Erik Broes <erikbroes@grum.nl>

paper-api/src/main/java/org/bukkit/event/server/ServerListener.java

@@ -30,4 +30,8 @@ public class ServerListener implements Listener {
      */
     public void onServerCommand(ServerCommandEvent event) {
     }
+
+    // Prevent compilation of old signatures TODO: Remove after 1.4
+    @Deprecated public final void onPluginDisable(PluginEvent event) {}
+    @Deprecated public final void onPluginEnable(PluginEvent event) {}
 }