Rework ANC button click

Slice view would only be there as an "image" to show the button. Button
composable handles the actual click alongside the a11y stuff

Flag: aconfig new_volume_panel NEXTFOOD
Test: manual on the phone with a compatible headset and voice over. Open
Volume Panel and focus a11y button
Fixes: 338527799
Fixes: 338531016
Fixes: 338532731
Fixes: 338346889

Change-Id: I2053ba8dc5f882922d7fffdf5fe6d396e31d1ebc