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/TetherService.java

@@ -255,7 +255,7 @@ public class TetherService extends Service {
     }
 
     private void disableTethering(final int tetheringType) {
-        final TetheringManager tm = getSystemService(TetheringManager.class);
+        final TetheringManager tm = (TetheringManager) getSystemService(Context.TETHERING_SERVICE);
         tm.stopTethering(tetheringType);
     }