new_package: make subpackages work when %{source_name} and Name: disagree
    
    Remove %new_package dependency on %{source_name} when creating subpackages by
    suffix. This way those subpackages still work even when the packager set
    %{source_name} to a value and Name: to another.
    
    Arguably, the packager is severily conflicted, and does not know what he wants
    to achieve, but this case is easy enough to accomodate by tweaking the decision
    tree. So let’s just make things work instead of blaming the packager.