auto merge of #15165 : zookoatleastauthoritycom/rust/14148-Optimize-out-exhortations...

auto merge of #15165 : zookoatleastauthoritycom/rust/14148-Optimize-out-exhortations-about-being-careful-2, r=huonw

Yes, it is important to be careful, but repeated emphasis about it is probably
not helpful — it starts to sound like you came for a tutorial but found a
finger-wagging lecture.

Even after I removed a few of these comments, there are still several left in
the text. That's probably fine! A couple of mentions of how this is dangerous
and you ought to be careful may be a good reminder to the reader.

After making the edits, I reflowed the paragraphs that I had touched, using
emacs's "M-x fill-paragraph", with fill-column equal to 70.