Removed Coveralls references and configuration

[adamzap]

After some discussion, the Website WG decided that we no longer want to use Coveralls. A coverage report is generated when running make ci locally.

Closes #2172.

[ulgens]

Added my notes on #2172 (comment).

[tobiasmcnulty]

Looks good to me (if the Website WG decision remains to remove it). 📦

[ulgens]

Coveralls is a blocker now

#2172 (comment)

@django/mergers Let me check the config and what's causing the current issues. I'll try to come up with an answer about if there is something we can easily fix, in a day.

[ulgens]

Let me check the config and what's causing the current issues.

It seems that they are working fine now: #2172 (comment)

I added several comments under the related issue and the meeting notes, but to sum up, if we merge this, we will be removing a useful tool. Now that the service is working again, there is no urgency in this decision anymore. We can try to fix the integration or replace it with an alternative, such as CodeCov.

[tobiasmcnulty]

We're moving forward with removing Coveralls since it's broken and we weren't able to repair it. Its replacement may be taken up in a new issue. More discussion here: #2172 (comment)