Remove remaining "Item added to home screen" annoucement from talkback.

Based on https://b.corp.google.com/issues/383457529#comment5, we should remove all app annouced confirmation.

Bug: 386247991
Test: build
Flag: EXEMPT a11y bug fix
Change-Id: I0ba2e282a42c0785c8bdad1be23adf2bf90a44b3