Remove WindowTreeClient::OnWindowOpacityChanged

This is not used actually (nobody calls this method), and actually
this is not necessary at all. Simply removing it.

Bug: 940533
Test: build passes
Change-Id: I3bb3a588db35f68e4a6b1692ca9af31ffb3069e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1529631
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Jun Mukai <mukai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642029}
15 files changed