[Pre-RFC] `cargo package` should include fewer files by default

SwishSwushPow: > Automatically checking the tests as part of the packaging/publishing process has been discussed in this thread as well, but I fear it might be out-of-scope as well. I disagree, I think it is a strong argument against removing files by default until tests are run during publishing. Most crate authors are not aware, and because of the poor support today, crater and Linux distros are likely the only users of the tests currently. Let's not make that worse.