Remove unecessary `itertools` dependency #95

Job	Run time
rustfmt	4s
cargo test (stable, false, true, false)	55s
clippy	28s
cargo test (beta, false, true, false)	57s
cargo test (stable, false, true, true)	1m 43s
cargo test (nightly, true, true)	2m 49s
cargo test (1.58.0, false, false)	3m 19s
	10m 15s

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