"Traced running time" is misleading, should be called "estimated running time" instead or be removed

Our "traced" running time is computed by looking at sample timestamps, and by making guesses that a function isn't exited if no sample outside of it was observed between samples inside of it.
This means that it's based on samples and guesswork, and not based on instrumentation.

The word "tracing" is largely understood to mean "based on instrumentation" rather than "based on guesses".

I think "estimated running time" would be a much better term for this.

See #2962 for a case where the guess is really inaccurate.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-480)