xen: remove unnecessary code from dataplane/xen-block.c

xen: remove unnecessary code from dataplane/xen-block.c

Not all of the code duplicated from xen_disk.c is required as the basis for
the new dataplane implementation so this patch removes extraneous code,
along with the legacy #includes and calls to the legacy xen_pv_printf()
function. Error messages are changed to be reported using error_report().

NOTE: The code is still not yet built. Further transformations will be
      required to make it correctly interface to the new XenBus/XenDevice
      framework. They will be delivered in a subsequent patch.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Anthony Perard <anthony.perard@citrix.com>
---
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
v4:
 - Fix boilerplate

v2:
 - Leave existing boilerplate alone, other than removing the now-incorrect
   description