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 https://googleplex-android-review.googlesource.com/q/commit:2465326a187f11fefde17e667e9cf3fd890cdb57)
Merged-In: Ic607ab91e77bc660e3fccbc2390dd60151798ad7
Change-Id: Ic607ab91e77bc660e3fccbc2390dd60151798ad7