staging: most: remove code to destroy channel

This patch removes unnecessary code to destroy channel objects. It is
needed, because function most_stop_channel, which is indirectly
triggered by function most_deregister_interface, already destroys the
channels.

Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>