Add support to cpConverter to drop content-packages of PackageType.CONTENT from targetmodel

In cases where content packages are converted for scenarios with use of CompositeNodeStore to handle the immutable content the featureModels are supposed to only install the immutable part of the repository - therefore the content-packages of PackageType.Content should be droppable. They anyhow can't be omitted from scanning & parsing as the conversion of service users, CNDs etc. into repoinit is still supposed to happen.