Disable Python 2 builds on Fedora >= 30
This currently depends on the Python package oauth2client, which
currently has a dependency on the Python package keyring, which it only
uses for testing. The keyring package dropped support for Python 2 and
has been removed from Rawhide. This disables building of Python 2 builds
on affected versions of Fedora until ths situation is resolved.
Note: the oauth2client library is deprecated, and its replacements do
not depend on keyring. Once upstream has replaced it, Python 2 builds
can be reenabled, if they haven't been already. See upstream #6507.