Always calculate the category of a room

All the update triggers for the RoomListStore go through the `setRoomCategory` function, so by returning early we're not actually calculating where a room should be in the list.

src/stores/RoomListStore.js

@@ -479,12 +479,6 @@ class RoomListStore extends Store {
     _setRoomCategory(room, category) {
         if (!room) return; // This should only happen in tests
 
-        if (!this._state.orderImportantFirst) {
-            // XXX bail here early to avoid https://github.com/vector-im/riot-web/issues/9216
-            // this may mean that category updates are missed whilst not ordering by importance first
-            return;
-        }
-
         const listsClone = {};
 
         // Micro optimization: Support lazily loading the last timestamp in a room