Drop CircleCI

[jeromekelleher]

It doesn't look like CircleCI tests are doing a great deal more than what we're covering in GitHub actions. Keeping two different CI providers going is too much of a maintenance burden.

[jeromekelleher]

The things we're doing that we're not doing in GitHub actions are:

• Running C tests with coverage
• Compiling under clang
• Running C tests with valgrind
• Some testing of the lwt interface
• Running coverage tests on the low-level CPython code.

I think it's easier to just port these to GitHub actions.

Note that a lot of this used to be done in 32 bit also, but we stopped doing it a while back. We already do some testing on 32bit windows in the msys section on GitHub actions, which is sufficient IMO.

[molpopgen]

Is there a 32 bit ARM runner available? tskit-rust has had recent PRs from users to improve ARM64/Linux support, so it seems like some people are using some interesting hardware. There is a ubuntu/arm64 runner available but I haven't looked for 32 bit.

[jeromekelleher]

Just noting that circle CI has been turned off - we can close this issue once the remaining C tests have been ported to GitHub actions and the config has been deleted.