timeline: Don't change state when Timeline is cleared.

It is not really in its initial state since it should be ready to load
more events.

src/session/model/room/timeline/mod.rs

@@ -384,7 +384,6 @@ impl Timeline {
 
         imp.sdk_items.remove_all();
         imp.event_map.take();
-        self.set_state(TimelineState::Initial);
     }
 
     /// Get the event with the given key from this `Timeline`.