Proximity Auth: Remove kMultiDeviceApi flagging from ProxAuthWebuiHandler.

R=hansberry@chromium.org

Bug: 899324
Test: none
Change-Id: Iac6aacb1b40608d261d6c13b12fd37bfd6b0df8f
Reviewed-on: https://chromium-review.googlesource.com/c/1325393
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Commit-Queue: James Hawkins <jhawkins@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606865}
5 files changed