Simplify creating HTTP errors

[thewilkybarkid]

Contrary to its documentation, the http-errors module doesn't create a new error if it is already an HTTP error, so we don't need to check its type locally.

[giorgiosironi]

I'd like to try to write a characterization test given it's an undocumented behavior if this is not urgent - more for my learning than for likelihood of future breakages which is minimal.

[thewilkybarkid]

More meant that it doesn't replicate the same error, rather than being something that unexpected.

[nlisgo]

@thewilkybarkid is there a related open issue on the http-errors project. At least to address the documentation?

[thewilkybarkid]

Commented at jshttp/http-errors#37 (comment).