remove pip-compile-multi

[davidism]

Dependabot isn't compatible with it, it always uses pip-compile directly, which produces different output (different header without update hash, all requirements inline). I want to use pip-compile-multi since it's convenient and has a pre-commit hook. If Dependabot fixes compatibility (dependabot/dependabot-core#536) I can add it back in.

See discussion in #159. CC @peterdemin

[peterdemin]

Hi @davidism, I did some experiments with GitHub Actions and I found an alternative to dependabot, that suites my needs:
https://github.com/peterdemin/pip-compile-multi/blob/master/.github/workflows/pipcompilemulti.yml
It runs pip-compile-multi weekly and creates a PR if there were changes to lock files.
Let me know what you think 🙏
Comparing to dependabot:
Pros:

• More control of the locking process. Allows creating both .txt and .hash files, for example.
• Allows locking platform-specific dependencies, like atomicwrites, which is pytest dependency under win32.
  Cons:
• Not aware of existing PRs, so if repo is left unattended, PRs tend to pile-up.
• Needs long GitHub Actions config file.

I want to beta-test it with you and then advertise to the public in README.

[davidism]

Can you open an issue on pip-compile-multi for discussion and ping me? I'm interested in this but we should discuss it in a dedicated place.