Preprocess dist-info/RECORD file in %install and remove it.
    
    According to PEP 627, the RECORD file is optional and
    doesn't make sense to keep it for system packages. Moreover,
    its absence should indicate to other tools like pip that
    they should not touch such packages.
    
    Now, we process content of all RECORD files to one
    pyproject-record (JSON) which is then used in
    %pyproject_save_files. That way, we can remove the original
    files in %pyproject_install and keep their content for
    later.
    
    PEP 627: https://www.python.org/dev/peps/pep-0627/#optional-record-file