In #12791 we discovered that removing from __future__ statements from .pyx files is not as trivial as the python ones, since at the moment we cythonize with language_level set to 2 (default), which also gives a FutureWarning while cythonizing (the default will switch to 3).

We need to explicitly set the language level cython directives on our cython files, and remove the __future__ imports from them, and figure out other possible required changes.

Right now removing the future import from _random.pyx results in tests failing.