WebBluetooth tests should be owned by content/browser/bluetooth OWNERS

Bug: None
Change-Id: I77b07c01393b54da1fa406eb9908573a104cac60
Reviewed-on: https://chromium-review.googlesource.com/c/1398293
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Commit-Queue: Doug Turner <dougt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620553}