Get rid of succ & fail marks on rate summary

[joanlopez]

What?

It replaces the use of succ & fail marks (✓/✗) for rate metrics on summary, in favor of the text: {success} out of {total}.

Note: the check summary remains the same, as for checks there's no ambiguity on the use of ✓ and ✗.

Why?

Because as discussed in https://github.com/grafana/k6/issues/2306 and https://github.com/grafana/k6/pull/3656, the current form is sometimes confusing, because the metric may have either a "positive" meaning (like successful requests) or a "negative" meaning (like failed requests), for which the use of ✓ may result in confusions, especially for the latter.

Checklist

• [X] I have performed a self-review of my code.
• [X] I have added tests for my changes.
• [X] I have run linter locally (make lint) and all checks pass.
• [X] I have run tests locally (make tests) and all tests pass.
• [X] I have commented on my code, particularly in hard-to-understand areas.

Related PR(s)/Issue(s)

Closes https://github.com/grafana/k6/issues/2306

Second iteration of https://github.com/grafana/k6/pull/3656, based on what was discussed there.