Remove mentions of managed pointers from the tutorial

[bstrie]

Their continued existence in the tutorial is causing confusion over what the status of this feature is. Let all the world know that managed pointers are relegated to the dustbin of history!

[thestinger]

It's unclear to me if the tutorial is being rewritten from scratch by Mozilla. There's not much motivation for anyone to work on it if it's just going to be thrown out.

[bstrie]

That may be true, but if a good samaritan wanted to do just enough work to delete mentions of them from the current tutorial, it would not be unappreciated.

[ckendell]

Hi, I am the one who asked about this initially. I have started to work on it now.

[brson]

At this point I do think it's worthwhile to keep maintaining the tutorial. Even if it doesn't survive as the tutorial, it does contain a lot of information that will end up disseminated elsewhere.

[kud1ing]

Not maintaining the tutorial leads to a growing collection of inaccurate or wrong information.
Removing it could give newcomers a better first-time experience of Rust.