Revert "Merge pull request #21704 from Cwiiis/bug1038185-close-utility-tray-transition"

This reverts commit 6bfbb48a79302c59220d83acfe896ea0abcf5aab, reversing
changes made to 8c0db75e19f1faf1de47733cfac9b05d988fee28.
Revert "Bug 1038698 - Disable intermittent test_a11y_utility_tray_visibility.py for TBPL"

This reverts commit 7e8c5220a51b631524b2e528766b820a92a05c9b.