Garbage collect unused and unsupported VGPU_types

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Simplify VGPU_type GC with new datamodel relations

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Merge pull request #1407 from simonjbeaumont/gc-vgpu-types

Garbage-collect unused and unsupported VGPU_types