Remove selection tracker workaround

app/src/main/java/eu/faircode/email/FragmentMessages.java

@@ -441,24 +441,12 @@ public class FragmentMessages extends FragmentBase {
                 @Override
                 public void onSelectionChanged() {
                     SelectionTracker tracker = selectionTracker;
-                    if (tracker == null)
+                    if (tracker == null) // destroyed
                         return;
 
                     FragmentActivity activity = getActivity();
-                    if (activity != null) {
-                        try {
-                            ViewModelMessages modelMessages = ViewModelProviders.of(activity).get(ViewModelMessages.class);
-                            if (tracker.hasSelection())
-                                modelMessages.removeObservers(viewType, getViewLifecycleOwner());
-                            else
-                                modelMessages.observe(viewType, getViewLifecycleOwner(), observer);
-                        } catch (IllegalStateException ex) {
-                            // getViewLifecycleOwner
-                            Log.w(ex);
-                        }
-
+                    if (activity != null)
                         activity.invalidateOptionsMenu();
-                    }
 
                     if (tracker.hasSelection()) {
                         swipeRefresh.setEnabled(false);