When expanding diff lines and leaving suggestion comments,
eventually, they showed as unnapliable
even with no changes in the diff.

It happened given the `DiffNote#supports_suggestion?` check was
being made at `Suggestion#appliable?` in the discussions iteration.

The problem with `DiffNote#supports_suggestion?` as it is that
it uses `Position#diff_file`, which has a RequestStore "cache".

So for instance, if we have 3 comments in expanded diff lines
for the same diff file, just the _first_ expansion would be
considered, therefore, just the _first_ suggestion within
this set of comments on expanded lines would be
appliable.

All in all, we're able to simply remove this check from the
`appliable?` method given we already check if the note supports
suggestions uppon creation (`Suggestions::CreateService`).

As an extra outcome, we'll submit less Gitaly requests.