xapi: remove unused reference to Xenstore in balloon.ml

All the balloon data was being read from /sys, there is no xenstore
component. Also, remove the unused XIU logic since we're not using
xen-on-xen.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
rrdd: the exported rrdd interface shouldn't include types from the Xenctrl module

Otherwise generic uses of rrdd end up depending on xen, for no reason.
xapi: remove some unused 'open <Module>'s

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
rrdd: don't build xcp-rrdd etc in phase2

Phase 2 was intended only for building code generated in phase 1.
xapi: fetch host CPU, hypervisor information through the xenops interface

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