[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/deviceinfo/firmwareversion/FirmwareVersionDetailPreferenceController.java

@@ -49,7 +49,7 @@ public class FirmwareVersionDetailPreferenceController extends BasePreferenceCon
 
     public FirmwareVersionDetailPreferenceController(Context context, String key) {
         super(context, key);
-        mUserManager = (UserManager) mContext.getSystemService(Context.USER_SERVICE);
+        mUserManager = mContext.getSystemService(UserManager.class);
         initializeAdminPermissions();
     }