Workstation: Drop PackageKit-cached-metadata
    
    We are now putting cached metadata directly on the installer images
    during the image compose process.
    
    Matching spin-kickstarts change:
    https://git.fedorahosted.org/cgit/spin-kickstarts.git/commit/?h=f23&id=e07cfce2f1118a2052f91f6f5839657a73fd5a23