Extract //chromeos/system from //chromeos

This incldues removing all of //chromeos as a dependency in //ash and a
few other places.

It also includes moving kiosk_oem_manifest_parser.cc to
src/chromeos/system, which is the only code that uses it.

For misc. mechanical changes:
[email protected]

Bug: 918682
Change-Id: I92753c1fc7814a2b595ec8b162fb80a5ada3d73e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1561839
Commit-Queue: Steven Bennetts <[email protected]>
Auto-Submit: Steven Bennetts <[email protected]>
Reviewed-by: Dan Erat <[email protected]>
Reviewed-by: James Cook <[email protected]>
Cr-Commit-Position: refs/heads/master@{#651287}
23 files changed