remove setup_requirments

see pypa/pip#4880
because setuptools uses it's own logic to find the depends, when user use pip -i $mirror to install flask-mongoengine can cause a network error.

Author: 9nix00

setup.py

@@ -49,7 +49,6 @@ def get_version(version_tuple):
     packages=["flask_mongoengine", "flask_mongoengine.wtf"],
     include_package_data=True,
     tests_require=test_requirements,
-    setup_requires=test_requirements,  # Allow proper nose usage with setuptools and tox
     description=description,
     long_description=long_description,
     classifiers=[