[A11y] Remove class name changed, which is unused

A number of events were added in CL:1510772 without use cases, early
on when Microsoft was getting accustomed to the codebase, to ensure
that every potential property change had a matching event.

After talking with Microsoft, it appears that this event and others
were added in CL:1510772 without having any use cases in hand.
It's easy enough to re-add if necessary.

As discovered in CL:5367566, firing events for every possible
property change is an expensive proposition, and when possible we should limit change events to those with known or likely cases.

Bug: none
Change-Id: I0cad8c3ebf17c58d12f41fa602a6c69269fc6d79
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5367568
Commit-Queue: David Tseng <dtseng@chromium.org>
Auto-Submit: Aaron Leventhal <aleventhal@chromium.org>
Reviewed-by: Benjamin Beaudry <benjamin.beaudry@microsoft.com>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1274357}