nightly docs claim impl of both Send and !Send for Rc. (etc for Sync)

[pnkfelix]

The stable docs had a bug where they claimed that Rc implements Send and Sync.

The nightly docs are better, in that now they claim that Rc implements !Send and !Sync... unfortunately, they continue to also claim that Rc implements Send and Sync.

• https://doc.rust-lang.org/nightly/std/marker/trait.Send.html
• https://doc.rust-lang.org/nightly/std/marker/trait.Sync.html

cc @alexcrichton

[jooert]

Triage: This seems to be fixed now. However the docs still state three times that Rc implements !Send and !Sync (see #25061).

[alexcrichton]

Indeed!