Remove ExpandableNotificationRow#isBlockingHelperShowing

This property was a part of the _Blocking helper_ feature which no longer exists.

Bug: 271574712

Test: manually interact with notifications
Test: atest ExpandableNotificationRowTest NotificationGutsManagerTest NotificationGutsTest
Change-Id: Ib019bef7dd95c6a88038038633455f3ac0b115a4
6 files changed