[Settings] Convert to getSystemService(Class<T>)

Change to getSystemService(Class<T>) to align the capability with framework
part.

Bug: 179640862
Test: local
Change-Id: I1b4812044fc4876bec6645570049a60f9470dbbd

src/com/android/settings/wifi/WifiAPITest.java

@@ -64,7 +64,7 @@ public class WifiAPITest extends SettingsPreferenceFragment implements
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
 
-        mWifiManager = (WifiManager) getSystemService(WIFI_SERVICE);
+        mWifiManager = getSystemService(WifiManager.class);
     }
 
     @Override