Move //c/b/ui/ash/volume_controller_browsertest.cc to //c/b/ash/audio

Bug: b:359064071
Change-Id: If41437eb0d84b61cdd35fc2a6038c2f87ab22652
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5784244


Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1343908}