Exit code for --max-downloads

[weedy]

As a unix user I fundamentally disagree with how #852 went but that's history now.

That said I can't imagine why you would want to exit non-zero when you use --max-downloads.

I wanted maximum 8 files, you gave me 8 files. Then exited with an error.
How does this make sense?

[yan12125]

As a reference, this "feature" is added in 94fd320. I guess it's because script writers need to know the reason of exiting. Ping @phihag.

By the way, --max-downloads violation has already a non-default exit code 101.

[tommcintyre]

Agreed with @weedy, a nonzero exit code is not appropriate in this situation as I mentioned in another issue here: #13598 (comment)

A canonical way to do this could be via some stats/summary info, either printed out to the console or to a file in a computer-readable format; e.g. --write-summary-json wherever.json.