Python template: Fix PyPI name declaration
    
    `%global %pypi_name` would not expand correctly because of the extra %.
    
    Remove it, and switch to using `srcname` which is preferred now per
    
    https://docs.fedoraproject.org/en-US/packaging-guidelines/Python/#_source_files_from_pypi
    
    Signed-off-by: Michel Alexandre Salim <salimma@fedoraproject.org>