Drop out-of-date manual release upload doc bit

[jakirkham]

This is a hold over from when we uploaded binaries manually. We no longer need it now that releases are done on CI. So drop this text.

xref: #270 (comment)

cc @joshmoore

TODO:

• Unit tests and/or doctests in docstrings
• tox -e py39 passes locally
• Docstrings and API docs for any new/modified user-facing classes and functions
• Changes documented in docs/release.rst
• tox -e docs passes locally
• GitHub Actions CI passes
• Test coverage to 100% (Coveralls passes)

[joshmoore]

🎉