core: remove VdcObjectType from ActionGroup enum

VdcObjectType in ActionGroup enum is unused by any component.
Hence, removing it from the enum along with unused
'entityToActionGroupsMapping'.

Change-Id: Ib40e8aab37ea11c463f03e25e1e48495db17ca1e
Signed-off-by: Daniel Erez <derez@redhat.com>