usb: typec: altmode: Remove the notification chain

Using the generic notification chain is not reasonable with
the alternate modes because it would require dependencies
between the drivers of the components that need the
notifications, and the typec drivers.

There are no users for the alternate mode notifications, so
removing the chain and the API for it completely.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20200211112531.86510-6-heikki.krogerus@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>