Simplify event resolving logic

Although this commit introduces a race condition since an
event may only be half-resolved. A lock is thus needed,
but it depends on an event-loop to which we don't have
access in the class-level.

telethon/events/raw.py

@@ -27,7 +27,7 @@ class Raw(EventBuilder):
             self.types = tuple(types)
 
     async def resolve(self, client):
-        pass
+        self.resolved = True
 
     @classmethod
     def build(cls, update):