Drop ver.py source file and use python version macros
    
    The %{python2_version} and %{python3_version} macros are pre-defined, so
    we don't need to use ver.py to find the versions.
    
    Use shell variable for Python 3 ABI flags instead of global macro. This
    avoids errors when creating SRPMs or running rpmlint, because by
    delaying the command until the %build stage we can rely on python3-devel
    being installed.