SystemUI: cleanup fps info tile and service

* Properly check if fps info node exists and is readable
* Check for props while debugging logs
* Hard-code fps info read interval
* Remove unnecessary configuration global var
* Make isReading a stateless var
* Register / unregister lifecycle observer only if tile state is toggled

Signed-off-by: jhonboy121 <alfredmathew05@gmail.com>
Signed-off-by: Dmitrii <bankersenator@gmail.com>
2 files changed