Remove tracing-gum

[alexggh]

With jaeger tracing removed in #5875, the reason for tracing-gum existence is gone, so we should consider removing it as well.

See #5875 (review) for more details.

[AndreiEres]

If gum::warn_if_frequent! is the only reason that holds it we can handle it in another place imho.

[programskillforverification]

I would like to work on this

[Krayt78]

Do you guys still want that done ?