virt: stats: get rid of _getStatsInternal

it was used on just one place anyway.

Change-Id: I469759b86115d80bad62c3449fe9084d5f2e550b
Signed-off-by: Francesco Romani <fromani@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/26557
Reviewed-by: Dan Kenigsberg <danken@redhat.com>