Revert "Mark Desktop Windowing transitions flags as BUGFIX"

This reverts commit dbd2105b.

Bug: 379712483, 379713395, 379716189

Reason for revert: It's not possible to change a non-bugfix flag to bugfix: go/releasing-flag-gantry#is-this-flags-workflow-still-in-sync-with-the-aconfig-declaration

Change-Id: I27904f9fbe2ffd8b88ca9e78bfe1c046c56665f1