chore: prepare tokio-util 0.7.1 release

[djc]

The minimal versions fix from #4490 is required to bump h2, which is probably one of the more prominent tokio-util users.

We might want to wait to get #4520 and/or #4508 in, too?

[Darksonn]

The test failure you saw might be related to the removal of path dependencies. You'll probably need to remove it in more places, or not remove it at all.

[zys864]

#4525

[Darksonn]

Seems like there's still some issue with two versions of the tokio crate existing simultaneously.

[zys864]

Seems like there's still some issue with two versions of the tokio crate existing simultaneously.

Seems like there isn't two versions of the tokio crate existing simultaneously.

With the dependenies

[dependencies]
# tokio-util = { version = "0.7.0", features = ["codec"] }
tokio-util = { path="../tokio/tokio-util", features = ["codec"] }
tokio = { version = "1", features = ["io-util"] }

After run cargo +nightly update -Zminimal-versions;cargo check --all-features on h2

Compiling tokio v1.6.1
Checking tokio-util v0.7.1 (/home/*/PL/Rust/tokio/tokio-util)

Cargo will use the mini support version tokio-1.6.1,and without tokio-1.0.1existing.

[Darksonn]

Thanks.