Remove zip_safe=False flag from setup.py.

The flag only matters when installing from eggs
(https://setuptools.readthedocs.io/en/latest/setuptools.html#setting-the-zip-safe-flag)
which are mostly unused nowadays, and setuptools will still correctly
infer that matplotlib is not "zip_safe" based on the presence of
extension modules even when zip_safe=False is not explicitly set.

Author: anntzer

setup.py

@@ -288,9 +288,5 @@ def run(self):
         install_requires=install_requires,
         setup_requires=setup_requires,
 
-        # matplotlib has C/C++ extensions, so it's not zip safe.
-        # Telling setuptools this prevents it from doing an automatic
-        # check for zip safety.
-        zip_safe=False,
         cmdclass=cmdclass,
     )