bluetooth: Always use DBusThreadManagerLinux or DBusThreadManager

We always end up using DBusThreadManagerLinux on Linux and
DBusThreadManager on Chrome OS. Rather than having clients pass
these when initializing BluezDBusThreadManager, have
BluezDBusThreadManager choose which one to use based on the OS.

This puts the logic for choosing which one to use in a single place.

Bug: 882771
Change-Id: I9c36eb9de8419fd5ac4bc6fbab3ded2738b33d91
Reviewed-on: https://chromium-review.googlesource.com/1237694
Reviewed-by: Sonny Sasaka <[email protected]>
Reviewed-by: Peter Beverloo <[email protected]>
Reviewed-by: Scott Violet <[email protected]>
Reviewed-by: Michael Giuffrida <[email protected]>
Commit-Queue: Giovanni Ortuño Urquidi <[email protected]>
Cr-Commit-Position: refs/heads/master@{#593730}
12 files changed