[CMake] Follow removal of testwrapper and testsubdomainset.

Remove commented lines for autotools, too.
[EntitySeed] Add missing interface method isValid() to EntitySeed wrappers

Thanks to Christoph Grüninger for reporting the problem!
Merge branch 'releases/2.3'

Forward-port fixes

* releases/2.3:
  [EntitySeed] Add missing interface method isValid() to EntitySeed wrappers
  [CMake] Follow removal of testwrapper and testsubdomainset.