adb: partially revert 3cf1b36e.

Revert the write_msg_lock part of commit 3cf1b36e. A write which hangs
will hold onto the mutex, preventing the device kick from ever
happening, which also causes lots of other stuff to hang, due to Kick
being called with the transport lock taken.

Test: python test_devices.py
Change-Id: Ie7c958799c93cad287c32d6bbef30c07f40c2d51
3 files changed