core: Remove IsVdsGroupWithSameNameExist

IsVdsGroupWithSameNameExistQuery is not used anywhere in
the code, and hence should be removed.

This patch removes the following:
1. The IsVdsGroupWithSameNameExistQuery class
2. The IsVdsGroupWithSameNameExist constant representing
   it in VdcQueryType
3. The IsVdsGroupWithSameNameExistParameters class which
   was only used by the removed query class.

Change-Id: I45467851d4f11b3f94496974cf6665c7206daeb5
Signed-off-by: Allon Mureinik <amureini@redhat.com>