Change feature spec to use `data-qa` and remove unused `js-` qa selector
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The following discussion from !46406 should be addressed:
- I'd love to see this changed to a `data-qa` selector, as I think that's what is expected by the ~Quality team
- Also, if we're not using `js-file-title` here maybe it could be removed.
_spec/features/merge_request/user_views_diffs_spec.rb_
```
it 'expands all diffs' do
first('.diff-toggle-caret').click
```
issue