Revert async sessions from 3dd8b7c (breaks sync properties)

Such as ChatGetter.input_chat and SenderGetter.input_sender
which rely on the fact that access to the session file will
be synchronous.

telethon/client/auth.py

@@ -399,7 +399,7 @@ class AuthMethods(MessageParseMethods, UserMethods):
         self._self_input_peer = None
         self._state.pts = -1
         await self.disconnect()
-        await self.session.delete()
+        self.session.delete()
         return True
 
     async def edit_2fa(