Revert "Revert "Remove the fallback AddSupervisedUserActivity.""

This reverts commit a30b27657b.

Reason for revert: Now we can remove the fallback activity since the real flow is ready

Change-Id: Iecedbf588412547feecc6de36c89236097f8c236

src/com/android/settings/users/UserSettings.java

@@ -514,13 +514,6 @@ public class UserSettings extends SettingsPreferenceFragment
                 .setPackage(mConfigSupervisedUserCreationPackage)
                 .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
 
-        // TODO(b/209659998): [to-be-removed] fallback activity for supervised user creation.
-        if (getActivity().getPackageManager().resolveActivity(intent, 0) == null) {
-            intent
-                .setClass(getContext(), AddSupervisedUserActivity.class)
-                .setPackage(null);
-        }
-
         startActivity(intent);
     }