Drop setuptools as a runtime dependency

Because of the change from using setuptools.pkg_resources to using
importlib, we no longer need a runtime dependency on setuptools. It is
still required, however, for running setup.py.

certbot-dns-dnsimple/setup.py

@@ -10,7 +10,6 @@ install_requires = [
     # This version of lexicon is required to address the problem described in
     # https://github.com/AnalogJ/lexicon/issues/387.
     'dns-lexicon>=3.14.1',
-    'setuptools>=41.6.0',
 ]
 
 if os.environ.get('SNAP_BUILD'):