Remove userbot functionality

This has a lot of legacy and cruft so there may be some stuff I've
missed but this first pass is enough to get a clear separation.

discord/guild.py

@@ -2090,29 +2090,6 @@ class Guild(Hashable):
         payload['max_age'] = 0
         return Invite(state=self._state, data=payload)
 
-    @utils.deprecated()
-    def ack(self):
-        """|coro|
-
-        Marks every message in this guild as read.
-
-        The user must not be a bot user.
-
-        .. deprecated:: 1.7
-
-        Raises
-        -------
-        HTTPException
-            Acking failed.
-        ClientException
-            You must not be a bot user.
-        """
-
-        state = self._state
-        if state.is_bot:
-            raise ClientException('Must not be a bot account to ack messages.')
-        return state.http.ack_guild(self.id)
-
     def audit_logs(self, *, limit=100, before=None, after=None, oldest_first=None, user=None, action=None):
         """Returns an :class:`AsyncIterator` that enables receiving the guild's audit logs.