Remove an outdated comment from docs #2283

Job	Run time
codegen	33s
cargo bench	1m 16s
cargo +stable build	1m 10s
cargo clippy	37s
cargo +beta build	1m 20s
cargo +nightly build	1m 3s
cargo +1.36 build (futures-{core, io, sink})	2m 42s
cargo doc	27s
cargo hack check --feature-powerset	4m 17s
cargo fmt	19s
cargo minimal-versions build	47s
cargo miri test	9m 9s
cargo build --target thumbv7m-none-eabi	38s
cargo test -Z sanitizer=address	5m 26s
cargo build --target thumbv6m-none-eabi	40s
cargo test -Z sanitizer=memory	3m 24s
cargo test (ubuntu-latest)	4m 39s
cargo test -Z sanitizer=thread	3m 44s
cargo +1.56 build	2m 5s
cargo test (macos-latest)	10m 52s
cargo test (windows-latest)	6m 10s
cargo test (ubuntu-latest, aarch64-unknown-linux-gnu)	4m 31s
cargo test (ubuntu-latest, armv7-unknown-linux-gnueabihf)	8m 10s
cargo test (ubuntu-latest, armv5te-unknown-linux-gnueabi)	9m 1s
cargo test (ubuntu-latest, i686-unknown-linux-gnu)	5m 17s
	1h 28m 17s

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