Remove the server logic and add the interdomain transport

The server logic should live somewhere else (ideally in xen-unstable).
The interdomain (kernelspace) transport is needed by Mirage guests.

Signed-off-by: David Scott <dave.scott@citrix.com>
Remove CREDITS.md: this referred to the server logic

The protocol and clients have been rewritten.

Signed-off-by: David Scott <dave.scott@citrix.com>