Proximity Auth: Remove kMultiDeviceApi flagging in Messenger.

R=hansberry@chromium.org

Bug: 899324
Test: none
Change-Id: I500b7249e5d7d87b028c1446cfb28f4d4159f7df
Reviewed-on: https://chromium-review.googlesource.com/c/1325215
Commit-Queue: James Hawkins <jhawkins@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606496}
12 files changed