[CrOS MultDevice] Remove kEnableUnifiedMultiDeviceSetup from //ash.

The feature has already been rolled out, and the flag is no longer
necessary.

Bug: 912743
Change-Id: Id1ebc0476921b234869d3f355f410b568dcd616b
Reviewed-on: https://chromium-review.googlesource.com/c/1381149
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617305}
1 file changed