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/WifiUtils.java

@@ -83,7 +83,7 @@ public class WifiUtils {
         final DevicePolicyManager dpm =
                 (DevicePolicyManager) context.getSystemService(Context.DEVICE_POLICY_SERVICE);
         final PackageManager pm = context.getPackageManager();
-        final UserManager um = context.getSystemService(UserManager.class);
+        final UserManager um = (UserManager) context.getSystemService(Context.USER_SERVICE);
 
         // Check if device has DPM capability. If it has and dpm is still null, then we
         // treat this case with suspicion and bail out.