libertas: kill cleanup_cmdnode()

Move the wakeup into lbs_complete_command(), and leave the other bits
in __lbs_cleanup_and_insert_cmd() which was the only caller now anyway.

There are two remaining direct callers of lbs_cleanup_and_insert_cmd(),
and they are both fine without the wakeup.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>