Remove responders gem

[tvdeyen]

What is this pull request for?

We don't need a gem for responding with JSON from a Rails controller.

Notable changes (remove if none)

Removes a not actually maintained and necessary dependency.

Checklist

• [x] I have followed Pull Request guidelines
• [x] I have added a detailed description into each commit message

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.96%. Comparing base (98293af) to head (71ffa5d).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2901 +/- ## ========================================== - Coverage 95.96% 95.96% -0.01% ========================================== Files 230 230 Lines 6269 6267 -2 ========================================== - Hits 6016 6014 -2 Misses 253 253 ```

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