Fix path-based dependencies
    
    Installation path macros must not be used in file dependencies:
    
    https://docs.fedoraproject.org/en-US/packaging-guidelines/#_file_and_directory_dependencies
    
    Furthermore, while libxslt (xsltproc) is always in /usr even in flatpak
    builds as it is part of the runtime, opensp (nsgmls) is built in /app as
    a dependency of libofx for various financial applications.  Therefore,
    no assumptions should be made regarding its location.