Drop Python 2 compatibility
    
    It was recently discovered that our usage of SafeConfigParser no longer
    works in Python 3.12.  This class was actually renamed to ConfigParser
    all the way back during Python 3.2.  There are still differences in
    Python 2.  Rather than adding conditionals for which name to import
    between Python 2 and 3, it is easier to just drop Python 2
    compatibility.  This also removes the need for the six dependency.
    
    https://docs.python.org/3.2/whatsnew/3.2.html#configparser