Hotfix: remove extra unthunk_tangent methods

[ToucheSir]

Fixes #30.

PR Checklist

• [ ] Tests are added
• [ ] Documentation, if applicable

[juliohm]

@ToucheSir could you please conclude this hotfix? This issue is affecting various packages I maintain, making it hard to release new versions in packages that depend on Zygote.jl

[ToucheSir]

There were two blockers to getting this merged:

1. The TagBot and Documenter configuration here had completely bitrotted. I had to spend a good amount of time updating those to work, otherwise any new releases would be incomplete.
2. There's a mysterious downstream failure with DiffEqFlux that didn't happen before this PR. I have no idea why, and if re-running CI doesn't fix it then I need help figuring out the root cause. Otherwise we'll end up merging a bugfix release which creates different bugs.

[juliohm]

As far as I understand it, the changes you introduced today broke downstream packages that were not broken before. So undoing these changes could be the safest hotfix.

A new PR could then be started to reintroduce the changes with more coverage tests. That way people can continue their work downstream while ZygoteRules.jl gets fixed.

[ToucheSir]

So undoing these changes could be the safest hotfix.

Just to clarify, that is precisely what this PR does. The problem is not a lack of coverage, but that existing downstream coverage tests started failing.

However, after much digging I've now determined that there were no downstream CI runs post Zygote 0.7 which would've shown the error we see here. CompatHelper is partly to blame because it doesn't run GH Actions CI by default. So I'm merging this as-is. Let me know if you still run into precompilation issues.

[juliohm]

I am still unable to precompile packages that depend on Zygote.jl:

] activate --temp
] add CoordRefSystems

WARNING: Method definition unthunk_tangent(ChainRulesCore.AbstractThunk) in module ZygoteRules at /home/juliohm/.julia/packages/ZygoteRules/KF1B6/src/adjoint.jl:40 overwritten in module Zygote at /home/juliohm/.julia/packages/Zygote/59YyM/src/compiler/chainrules.jl:4.
│  ERROR: Method overwriting is not permitted during Module precompilation. Use `__precompile__(false)` to opt-out of precompilation.

[ToucheSir]

Can you wait until after JuliaRegistries/General#123376 has been merged (+ some time for the usual package server propagation) and try?

[juliohm]

Sorry, I thought that the latest release from 3 hours ago already included the fix. Will wait and retry. Thanks.

[ToucheSir]

Oh sorry, I see where the confusion came from. That release was me getting TagBot to work again, hence the very recent timestamp which made it look like it was for this PR instead. I just tested your MWE of ] adding CoordRefSystems and it works locally for me without errors, so hopefully this has resolved that issue.

[juliohm]

Thank you! I confirm the issue has been resolved in various downstream packages.