Make AirplaneModePrefController.isAvailable static.

Allows calling without instantiating the pref controller.
Also some minor cleanup of MobileNetworkPrefController.

Bug: 62022517
Test: robotests
Change-Id: I34ff5d3729d06158bff3cc125de4c114bf4861d5

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

@@ -45,7 +45,6 @@ public class AirplaneModePreferenceController extends PreferenceController
 
     private final Fragment mFragment;
     private final MetricsFeatureProvider mMetricsFeatureProvider;
-    private final PackageManager mPackageManager;
     private AirplaneModeEnabler mAirplaneModeEnabler;
     private SwitchPreference mAirplaneModePreference;
 
@@ -53,7 +52,6 @@ public class AirplaneModePreferenceController extends PreferenceController
     public AirplaneModePreferenceController(Context context, Fragment hostFragment) {
         super(context);
         mFragment = hostFragment;
-        mPackageManager = context.getPackageManager();
         mMetricsFeatureProvider = FeatureFactory.getFactory(context).getMetricsFeatureProvider();
     }
 
@@ -88,7 +86,11 @@ public class AirplaneModePreferenceController extends PreferenceController
 
     @Override
     public boolean isAvailable() {
-        return !mPackageManager.hasSystemFeature(PackageManager.FEATURE_TELEVISION);
+        return isAvailable(mContext);
+    }
+
+    public static boolean isAvailable(Context context) {
+        return !context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_TELEVISION);
     }
 
     @Override