Remove notification content from icon a11y

The content can be read when the full cards are visible

Test: StatusBarIconViewTest
Test: enable talkback, highlight icons
Flag: EXEMPT bug fix
Bug: 338024220
(cherry picked from commit e55a350c)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:9d00ab315dd7d661e71b5fcc51152ced2b2ae28a)
Merged-In: I3d3b7329c187808a28663aab16838a93a288b051
Change-Id: I3d3b7329c187808a28663aab16838a93a288b051