Broken links of `&mut self` in Deref sections

[tesuji]

In https://doc.rust-lang.org/nightly/std/io/struct.IoSlice.html#method.as_ptr, the link to as_mut_ptr is broken.
Even though there is as_mut_ptr item in the sidebar.

This maybe one reason make #32129 happens.

[tesuji]

Maybe if there are no DerefMut<Target = U> for type T:

• hide &mut self methods on sidebar
• Any refs to &mut self in U shouldn't be fragment links only.

[nbdd0121]

What would be sensible way to deal with &mut self ref in U though? It doesn't make much sense to point to the doc in U as well because without DerefMut impl you these methods aren't usable.

[lolbinarycat]

triage: such items are now hidden from the "methods from Deref" section, and the link is no longer broken.