Tidy xend-config.sxp, removing entries that haven't been used since the

Tidy xend-config.sxp, removing entries that haven't been used since the
hotplugging stuff was introduced (block-*, console-port-base, console-address)
and introducing entries for options that have been present for ages
(xend-{http,unix,relocation}-server, xend-unix-path, xend-relocation-address,
enable-dump).  Remove vif-antispoof, as Vifctl no longer passes this option
down.

Made the xend-relocation-server default to no, as this is a potential security
hole and so must be turned on explicitly.

Signed-off-by: Ewan Mellor <ewan@xensource.com>