Get rid of Suggestion.translator_comment_f

[julen]

In 62e745e a translator_comment_f field was added to the Suggestion model, it has never been used though.

While there's a common will to improve the workflow for suggestions —for instance allowing reviewers to give a reason (#2596)—, at the moment this field is useless and there's no problem to bring anything similar back when enhancing the suggestions functionality.

[unho]

+1 Storing review messages on a field with a different name would be better.

[julen]

To clarify: I'm not proposing a rename, but getting rid of the field. If it's necessary any field like that can be added when working on improving the actual workflow.

[unho]

To clarify: I agree with removing the field.