Arbitrary self types v2: update reference.

[adetaylor]

Part of rust-lang/rust#44874

[adetaylor]

@rustbot label +S-waiting-on-author -S-waiting-on-review

[Skgland]

Wouldn't the point

• [Methods] can take [Type<T>] as a receiver.

for Box<T>, Rc<T>, Arc<T> and Pin<T> no longer be special about these types with
the Receiver trait being stabilized? And as such that bullet point and in turn the latter three Types should be removed from the list?

https://github.com/rust-lang/reference/pull/1699/files#diff-90d122e8e582daf4ac75c86e4be63d9c91e7bc7cc6144bad4d62de7332eddf35R15-R29