Revert "Add a way to stash/unstash transient taskbar."

This reverts commit 6163e2d3.

Reason for revert: Part of Platinum+DM rotation for testing as likely culprit for breaking launcher tests on tablet. Won't be commited until proven otherwise.

Bug: 256988243
Bug: 256987492
Change-Id: I21b3561f489e17c48131d2223a7d90267968232f