GitLab

This CL:
- Adds !defined(USE_ATHENA) ifdefs where Ash is used.
- Stops compiling KeyboardOverlayUI in Athena because it is not necessary
- Stops compiling in Athena for simplicity:
   DisplayOptionsHandler, PowerHandler, FirstRunUI

BUG=426561
TEST=None
TBR=oshima,estade,stevenjb

Review URL: https://codereview.chromium.org/684143003

Cr-Commit-Position: refs/heads/master@{#302376}