[QsRevamp Clean Up] remove the expand/collapse behavior
from the unified_system_tray_controller

Also removed the corresponding preference recording, metrics logging.

OBSOLETE_HISTOGRAMS=ChromeOS.SystemTray.AnimationSmoothness
and SystemTrayTransitionType in the suffixes list

Bug: b/305075031
Test: Manually verified and the dead tests has been removed.
Change-Id: I752adfa72bf598fd3977548663cb336c638be3cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5014872
Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Chad Duffin <chadduffin@chromium.org>
Commit-Queue: Jiaming Cheng <jiamingc@chromium.org>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1223150}