Use poll_fn from the standard library

[eduardosm]

Motivation

std::future::poll_fn has been stabilized in Rust 1.64 and Tokio's MSRV is now 1.70.

Solution

poll_fn defined in tokio and tokio-stream have been removed and replaced with std's version. Uses of futures::future::poll_fn have also been replaced.

[Darksonn]

Perhaps it makes more sense to just have the select! macro use the std poll_fn directly?

[eduardosm]

There are already other items from std being imported in macros::support:

tokio/tokio/src/macros/support.rs

Lines 11 to 13 in 1166ecc

	pub use std::future::{Future, IntoFuture};
	pub use std::pin::Pin;
	pub use std::task::Poll;

[Darksonn]

Fair point.

[Darksonn]

Thanks.