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/WifiAPITest.java

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