hw/xen: Remove deadcode

hw/xen: Remove deadcode

xen_be_copy_grant_refs is unused since 2019's
  19f87870ba ("xen: remove the legacy 'xen_disk' backend")

xen_config_dev_console is unused since 2018's
  6d7c06c213 ("Remove broken Xen PV domain builder")

Remove them.

Signed-off-by: Dr. David Alan Gilbert <dave@treblig.org>
Acked-by: Anthony PERARD <anthony.perard@vates.tech>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@amd.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>