[libtaskmanager] Remove a poorly conceived optimization

The LauncherTasksModel tried to avoid a model reset by making certain
assumptions to save a few cycles. Ultimately this was misguided, in-
correctly not evicting the internal app data cache as well as causing
a lot more work in the view trying to compute layout deltas and some-
times causing a few frames of ugly animations.

There likely _is_ some optimization potential here, but it needs to
be done smarter later on.

(cherry picked from commit 40d7df210f)

libtaskmanager/launchertasksmodel.cpp

@@ -475,31 +475,14 @@ void LauncherTasksModel::setLauncherList(const QStringList &serializedLaunchers)
 
     if (newLaunchersOrder != d->launchersOrder
         || newActivitiesForLauncher != d->activitiesForLauncher) {
-        // Common case optimization: If the list changed but its size
-        // did not (e.g. due to reordering by a user of this model),
-        // just clear the caches and announce new data instead of
-        // resetting.
-        if (newLaunchersOrder.count() == d->launchersOrder.count()) {
-            d->appDataCache.clear();
+        beginResetModel();
 
-            std::swap(newLaunchersOrder, d->launchersOrder);
-            std::swap(newActivitiesForLauncher, d->activitiesForLauncher);
+        std::swap(newLaunchersOrder, d->launchersOrder);
+        std::swap(newActivitiesForLauncher, d->activitiesForLauncher);
 
-            emit dataChanged(
-                    index(0, 0),
-                    index(d->launchersOrder.count() - 1, 0));
+        d->appDataCache.clear();
 
-        } else {
-            beginResetModel();
-
-            std::swap(newLaunchersOrder, d->launchersOrder);
-            std::swap(newActivitiesForLauncher, d->activitiesForLauncher);
-
-            d->appDataCache.clear();
-
-            endResetModel();
-
-        }
+        endResetModel();
 
         emit launcherListChanged();
     }