Cleanup some garden-o-matic cruft and dead code.

The biggest change is removing RelativeTime. We were creating these,
but not doing anything with them. These were also the only
things that ever called setIndex on Notification, so we can remove
index/setIndex from Notification.

The rest of the patch is just removing dead code.

NOTRY=true

Review URL: https://codereview.chromium.org/336033002

git-svn-id: svn://svn.chromium.org/blink/trunk@176156 bbb929c8-8fbe-4397-9dbb-9b2b20218538