Proximity Auth: Remove final kMultiDeviceApi flagging.

R=hansberry@chromium.org

Bug: 899324
Test: none
Change-Id: Ic9ea29d50b11385db9641a0d106a80b68ea0b1da
Reviewed-on: https://chromium-review.googlesource.com/c/1327417
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: James Hawkins <jhawkins@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606949}
6 files changed