Remove pytest-runner from setup_requires

setup.py

@@ -5,7 +5,6 @@
 import sys
 import setuptools
 from distutils.sysconfig import get_config_vars
-from pkg_resources import parse_version
 from setuptools import Distribution as _Distribution, setup
 from setuptools.command.build_ext import build_ext as _build_ext
 import errno
@@ -144,14 +143,6 @@ def get_objects():
 with open(os.path.join(base_dir, "README.rst")) as f:
     long_description = f.read()
 
-# On some systems(e.g. Debian 8, CentOS 7) the setuptools package is very old.
-# We try to install an old version of pytest-runner without setuptools_scm dependency.
-# See: https://github.com/pytest-dev/pytest-runner/blob/master/CHANGES.rst
-if parse_version(setuptools.__version__) < parse_version("12"):
-    setup_requires = ["pytest-runner<2.4"]
-else:
-    setup_requires = ["pytest-runner"]
-
 
 setup(
     name=about["__title__"],
@@ -185,11 +176,11 @@ def get_objects():
     ],
     setup_requires=[
         "cffi>=1.0.0",
-    ] + setup_requires,
-    tests_require=[
-        "pytest",
     ],
     extras_require={
+        "test": [
+            "pytest",
+        ],
         "docstest": [
             "doc8",
             "readme_renderer >= 16.0",