Fix App header buttons announcing name twice

There were two versions of the same linearlayout that were a11y
focusable for each app header button, due to how the XML was imported,
so now setting one layer to  not important for accessibility, so only
the clickable layer will be noticed

Fix: 398128081
Test: open app in desktop windowing, open app chip menu, turn on
talkback and try to swipe through button
Flag: EXEMPT bugfix

Change-Id: I6481aa412325ad2917938b91a3f2eae6c0d73c11