Make the unversioned %__python macro error
    
    See https://fedoraproject.org/wiki/Changes/PythonMacroError
    
    While doing it, make %python macros more consistent with %python3 macros,
    mostly wrt whitespace but also to use python -m pip over plain pip etc.
    
    One significant change is the removal of sleeps from python macros,
    this could affect packages that use python macros to build for Python 2
    while also using python3 macros to build for Python 3.
    In reality, I consider that unlikely. The sleep in python2 macros stays.
    
    The --strip-file-prefix option was already removed from %pyX_install_wheel
    but we forgot to remove it from %py_install_wheel.