[EoC] Remove support for reverse scroll triggering

We're no longer experimenting with reverse scroll triggering, so remove
support for:
 - reverse scroll triggering
 - slim peek
 - peek conditions (apart from delay, which we may use later)

BUG=859292,876943,885331

Change-Id: Ibe962d6ece4340eb7b57784bbe078cc0847de728
Reviewed-on: https://chromium-review.googlesource.com/1236453
Reviewed-by: Becky Zhou <huayinz@chromium.org>
Reviewed-by: Filip Gorski <fgorski@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593386}
29 files changed