Revert "[Settings] Support getSystemService(Class<T>)"

This reverts commit d5ccde31a8.

Reason for revert: failure on test cases

Change-Id: I0a179a6ebb5ef1dec566ce6e8facd5f3b82d7c8a

src/com/android/settings/wifi/tether/WifiTetherSettings.java

@@ -110,7 +110,7 @@ public class WifiTetherSettings extends RestrictedDashboardFragment
     @Override
     public void onAttach(Context context) {
         super.onAttach(context);
-        mWifiManager = context.getSystemService(WifiManager.class);
+        mWifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
         mTetherChangeReceiver = new TetherChangeReceiver();
 
         mSSIDPreferenceController = use(WifiTetherSSIDPreferenceController.class);