[Switch Access] Clean up preferences.js

Bug: 864809
Change-Id: I8529852f4337dd095498f9f6b7359e3cd8dd2a53
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1578024
Reviewed-by: Akihiro Ota <akihiroota@chromium.org>
Commit-Queue: Anastasia Helfinstein <anastasi@google.com>
Cr-Commit-Position: refs/heads/master@{#654276}
8 files changed