[Multidevice] Do not attempt write-w/o-response to phone.

The Multidevice GATT characteristic hosted by the phone does
not support write-without-response.

Bug: b:158501694
Change-Id: I9b946cd179fbad21e7f0ec528bce9355b01334e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2238617
Reviewed-by: Sonny Sasaka <sonnysasaka@chromium.org>
Reviewed-by: James Vecore <vecore@google.com>
Commit-Queue: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#777164}