This was duplicating content in setup.py (and the two had gotten out of
sync, listing different versions for scipy).
According to the Python Packaging User Guide
(https://packaging.python.org/en/latest/discussions/install-requires-vs-requirements/),
the `install_requires` specifies what a project minimally needs to run
correctly, while the requirements.txt file contains an exhaustive list
of pinned versions for the purpose of repeatable installations of a
complete environment. Cleanlab is a Python package that users will `pip
install`, so we don't need a requirements.txt.
Some related projects like scikit-learn don't have a requirements.txt,
and others that do have such a file use it for a different purpose, e.g.
PyTorch and Keras use the file to list dev dependencies.
Ulyana