Refine the check restriction function in WifiEntryPreference

- Move checkRestrictionAndSetDisabled function from WifiEntryPreference to necessary child-classes to avoid impacting other child-classes such as SavedAccessPointsPreference.

- Avoid adding ShadowRestrictedPreference to the unnecessary test class.

Bug: 233871529
Test: manual test
make RunSettingsRoboTests

Change-Id: Ia2145401558b293b5f4eaa0860f83b7d3bbab548

tests/robotests/src/com/android/settings/wifi/WifiEntryPreferenceTest.java

@@ -40,13 +40,11 @@ import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 import org.robolectric.RobolectricTestRunner;
 import org.robolectric.RuntimeEnvironment;
-import org.robolectric.annotation.Config;
 
 import java.util.ArrayList;
 import java.util.List;
 
 @RunWith(RobolectricTestRunner.class)
-@Config(shadows = ShadowRestrictedPreference.class)
 public class WifiEntryPreferenceTest {
 
     private Context mContext;