greybus: hd: remove connection-create/destroy callbacks

These host-driver callbacks were intended to allow host drivers to
prepare a cport, something which can now be handled by the cport
enable/disable callbacks instead.

The current create/destroy are somewhat confusingly named as they were
not supposed to create or destroy connections. They were however called
from the unrelated helper functions that do create and destroy SVC
connections.

Furthermore, no errors were returned should the create callback fail,
which should have caused the connection initialisation to fail.

Remove these unused callbacks for now, and let us use the cport
enable/disable callbacks that should be able handle all host cport
initialisation (possibly after also adding an interface to provide
information for endpoint-cport mapping).

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>