core: Remove unused GetVmsByVmTemplateGuidQuery

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

This patch removes the following:
1. The unused GetVmsByVmTemplateGuidQuery class.
2. The GetVmsByVmTemplateGuidParameters class used by the
   aforementioned query class. All its meaningful methods (i.e., getId()
   and the constructor from Guid were pulled up to
   GetVmTemplatesDisksParameters which used to extend it.
3. The GetVmsByVmTemplateGuid constant in VdcQueryType
   corresponding to the removed class.

Change-Id: Ieef493712c75bc386dce066f9774ffe83c1be8fa
Signed-off-by: Allon Mureinik <amureini@redhat.com>