[Provider Model] Internal cleanup - remove Provider Model flag and deprecated legacy UI

Test: atest NetworkProviderCallsSmsFragmentTest, SubscriptionsPreferenceControllerTest
Bug: 197066557
Change-Id: I55e0fa2ca7317cd8c9d1bce7c229b8344f43cc92

src/com/android/settings/network/NetworkProviderCallsSmsFragment.java

@@ -100,8 +100,7 @@ public class NetworkProviderCallsSmsFragment extends DashboardFragment {
 
                 @Override
                 protected boolean isPageSearchEnabled(Context context) {
-                    return Utils.isProviderModelEnabled(context) &&
-                            context.getSystemService(UserManager.class).isAdminUser();
+                    return context.getSystemService(UserManager.class).isAdminUser();
                 }
             };
 }