remove setup_requires b/c it was problematic for conda-forge

Author: wholmgren

setup.py

@@ -45,7 +45,6 @@
                     'pytz',
                     'six',
                     ]
-SETUP_REQUIRES = ['pytest-runner']
 TESTS_REQUIRE = ['pytest', 'nose']
 
 CLASSIFIERS = [
@@ -96,7 +95,6 @@
       cmdclass=versioneer.get_cmdclass(),
       packages=PACKAGES,
       install_requires=INSTALL_REQUIRES,
-      setup_requires=SETUP_REQUIRES,
       tests_require=TESTS_REQUIRE,
       ext_modules=extensions,
       description=DESCRIPTION,