nix: Remove flake8 from test requirements.

pkgs/python-packages.nix

@@ -1418,7 +1418,7 b''
   };
   rhodecode-enterprise-ce = super.buildPythonPackage {
     name = "rhodecode-enterprise-ce-4.5.0";
-    buildInputs = with self; [WebTest configobj cssselect flake8 lxml mock pytest pytest-cov pytest-runner pytest-sugar];
+    buildInputs = with self; [WebTest configobj cssselect lxml mock pytest pytest-cov pytest-runner pytest-sugar];
     doCheck = true;
     propagatedBuildInputs = with self; [Babel Beaker FormEncode Mako Markdown MarkupSafe MySQL-python Paste PasteDeploy PasteScript Pygments Pylons Pyro4 Routes SQLAlchemy Tempita URLObject WebError WebHelpers WebHelpers2 WebOb WebTest Whoosh alembic amqplib anyjson appenlight-client authomatic backport-ipaddress celery channelstream colander decorator deform docutils gevent gunicorn infrae.cache ipython iso8601 kombu msgpack-python packaging psycopg2 py-gfm pycrypto pycurl pyparsing pyramid pyramid-debugtoolbar pyramid-mako pyramid-beaker pysqlite python-dateutil python-ldap python-memcached python-pam recaptcha-client repoze.lru requests simplejson waitress zope.cachedescriptors dogpile.cache dogpile.core psutil py-bcrypt];
     src = ./.;

setup.py

@@ -117,7 +117,6 b' test_requirements = ['
     'WebTest',
     'configobj',
     'cssselect',
-    'flake8',
     'lxml',
     'mock',
     'pytest',