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/client/telegrambaseclient.py

@@ -270,8 +270,6 @@ class TelegramBaseClient(abc.ABC):
 
         # Some further state for subclasses
         self._event_builders = []
-        self._events_pending_resolve = []
-        self._event_resolve_lock = asyncio.Lock()
         self._conversations = {}
 
         # Default parse mode