GitLab

Some a11y related source files were put directly under ash/system
or ash/system/unified while there's ash/system/accessibility.

TEST=trybot pass
BUG=none

Change-Id: I779b7791c582422451d0f8ef1d63ccadc0d40952
Reviewed-on: https://chromium-review.googlesource.com/c/1272918
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600653}