Removing focusability from all scrims in shade

This caused unnecessary catching focus when user opens shade and presses Tab key. Only 3rd press would actually show focus on the first actionable element (QS).
I don't think there's any use case when (a11y) focus would be useful on scrims as they are just coloring background and serve different roles depending on shade state.

Fixes: 311165439
Test: With keyboard connected, open shade, press Tab once and see focus immediately going to QS
Change-Id: Id2fb700f6799d2a6f8d0ea5fc56391cec342be6a