refactor: `TryFuture`s are `Future`s now, `into_future` is no longer need #2763

Job	Run time
cargo bench	20s
cargo +1.36 build (futures-{core, io, sink})	52s
cargo clippy	15s
cargo +stable build	20s
cargo doc	16s
cargo +beta build	23s
cargo hack check --feature-powerset	18s
cargo fmt	11s
cargo +nightly build	23s
cargo minimal-versions build	20s
cargo miri test	34s
cargo build --target thumbv7m-none-eabi	19s
cargo test -Z sanitizer=address	38s
cargo build --target thumbv6m-none-eabi	22s
cargo test -Z sanitizer=memory	37s
cargo test (ubuntu-latest)	17s
cargo +1.56 build	1m 29s
cargo test (macos-latest)	26s
cargo test (windows-latest)	40s
cargo test -Z sanitizer=thread	40s
cargo test (ubuntu-latest, aarch64-unknown-linux-gnu)	1m 15s
cargo test (ubuntu-latest, armv7-unknown-linux-gnueabihf)	58s
cargo test (ubuntu-latest, armv5te-unknown-linux-gnueabi)	39s
cargo test (ubuntu-latest, i686-unknown-linux-gnu)	35s
	13m 7s

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