Drop SNS support for children of hipposys:domain and hipposys:domainrule

The current node type definitions for hipposys:domainrule and hipposys:domain are:

[hipposys:domainrule] > nt:base
+ * (hipposys:facetrule) = hipposys:facetrule multiple
- hipposys:description (string)

[hipposys:domain] > nt:base
+ * (hipposys:domainrule) = hipposys:domainrule multiple 
+ * (hipposys:authrole) = hipposys:authrole multiple
- hipposys:description (string)

Technically and functionally however there is no reason to need or use or support SNS children for hipposys:domainrule or hipposys:domain.

With the migation to HCM (YAML) this already has been taken care of for the CMS product configuration, and the esv2yaml migration tool will likewise (mostly) do this automatically for end projects (HCM-89).
So what remains to do is:

• enforcing these constraints through the CND definitions by updating hipposys.cnd (scope of this issue):

  [hipposys:domainrule] > nt:base
  + * (hipposys:facetrule) = hipposys:facetrule
  - hipposys:description (string)
  
  [hipposys:domain] > nt:base
  + * (hipposys:domainrule) = hipposys:domainrule
  + * (hipposys:authrole) = hipposys:authrole
  - hipposys:description (string)

• adjust unit-tests which not yet do honor these new restrictions
• ensure existing repository data is properly migrated/fixed at startup (REPO-1644)