GitLab

This wipes out obsolete references to Service Manager in service-related
documentation and replaces it with simpler docs reflecting the new
service model.

Bug: None
Change-Id: Iab5662bcc48b34954a9003532cd407058e470282
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2063773
Commit-Queue: Ken Rockot <rockot@google.com>
Reviewed-by: Oksana Zhuravlova <oksamyt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742677}