Remove the runtime guide.

Now that libgreen is gone, this is all wrong.

Fixes #17923
remove shootout warnings
auto merge of #17936 : TeXitoi/rust/remove-shootout-warnings, r=alexcrichton

Only one warning remain, and I can't find a way to remove it without doing more bound checks:

```
shootout-nbody.rs:105:36: 105:51 warning: use of deprecated item: use iter_mut, #[warn(deprecated)] on by default
shootout-nbody.rs:105             let bi = match b_slice.mut_shift_ref() {
```

using `split_at_mut` may be an option, but it will do more bound checking.

If anyone have an idea, I'll update this PR.
auto merge of #17928 : steveklabnik/rust/remove_runtime_guide, r=alexcrichton

Now that libgreen is gone, this is all wrong.

Fixes #17923
loader: suggest to set crate type explicitly

Now loader suggests to set crate type explicitly if it founds file with
name similar to crate name, but different extension.

This commit adds warning if loader found static library instead of rlib
or dylib. It fixes issue #14416.