Fixing light border around sticky key indicator

The solution is to remove default background color coming from theme.
This background can't be set to surfaceInverse because theme will not reload color on device theme change. It's easier to just manage all colors in Compose

Fixes: 328050514
Flag: ACONFIG com.android.hardware.input.keyboard_a11y_sticky_keys_flag TRUNKFOOD
Test: see indicator with light device theme
Test: switch device theme while indicator is showing
Change-Id: I9df157bd3dc623b9c821a55030f9c815caac1ee2