Switch to sp/mp init events (#404)

exp_util/module/async.lua

@@ -408,13 +408,10 @@ end
 local e = defines.events
 local events = {
     [e.on_tick] = on_tick,
+    [e.on_singleplayer_init] = Async.on_init,
+    [e.on_multiplayer_init] = Async.on_init,
 }
 
-local Clustorio = ExpUtil.optional_require("modules/clusterio/api")
-if Clustorio then
-    events[Clustorio.events.on_server_startup] = Async.on_init
-end
-
 Async._function_metatable.__call = Async._function_prototype.start_soon
 Async.events = events --- @package
 return Async