CA-111270: Document VM_guest_metrics.memory as holding no data.
Nothing has been written to this field since before George
(XS5.5 release in 2008). It was disabled in favour of the RRD
data sources.

Signed-off-by: Thomas Sanders <thomas.sanders@citrix.com>
CA-111269: Document VM_guest_metrics.disks as holding no data.
Nothing has been written to this field since before XenServer 5.0.

Signed-off-by: Thomas Sanders <thomas.sanders@citrix.com>
Merge pull request #1361 from thomassa/good-blank-vm-metrics

Docs-fix: VM_guest_metrics.disks and .memory were removed years ago.