Simplify Domainmodel example target platform

[LorenzoBettini]

The .target file of the Domainmodel example is exceedingly and uselessly complex: it uses slicer instead of planner, forcing to list all requirements, without any benefit. I guess that happened when @kthoms introduced several target platforms using the TPD DSL (something that was then removed). The TP should use planner and list many less features. I'll provide a PR