remove codecov.io integration

[ahmetb]

After switching fully to GitHub Workflows we no longer use Codecov.io. We
also didn't really get much out of it.

/assign @corneliusweig

[corneliusweig]

Can you add instructions to the readme how to get visual feedback for coverage? Like

go test -coverprofile=coverage.out
go tool cover -html=coverage.out

[ahmetb]

Aren't they the same for all go projects? Why need that?

[corneliusweig]

They are the same, yes. But we could still put it in our developer docs, just in case sbdy is not familiar with go and wants to contribute.

[ahmetb]

Honestly, not sure why would it occur people to do that. I suspect most contributors don't read dev docs in full –so I'm inclined to leave it out. We review for missing tests anyway.

[corneliusweig]

I sort of have a deja vu that we talked about once before. Let's leave as is until somebody complains :)
/lgtm
/approve

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