[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/WifiStatusTest.java

@@ -116,7 +116,7 @@ public class WifiStatusTest extends Activity {
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
 
-        mWifiManager = (WifiManager) getSystemService(WIFI_SERVICE);
+        mWifiManager = getSystemService(WifiManager.class);
 
         mWifiStateFilter = new IntentFilter(WifiManager.WIFI_STATE_CHANGED_ACTION);
         mWifiStateFilter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION);