Staging: hv: mousevsc: Now cleanup mousevsc_remove()

Now, cleanup mousevsc_remove(). The mouse driver once initialized only
receives data from the host. So, by closing the channel first in the
unload path, we can properly deal with inflight packets. So, we don't need
the machinery for managing the life-cycle of the mousevsc_dev object.
Get rid of the unnecessary code.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>