remove itertools #2789

Job	Run time
minimal	18s
msrv	51s
check-cfg	23s
docs	25s
quickchecking	22s
rustfmt-clippy	29s
test (ubuntu-latest, 9.0, 0, 0, 0, 0)	1m 47s
test (ubuntu-latest, 9.0, 0, 0, 1, 0)	1m 48s
test-book	5s
test-expectations (ubuntu-latest)	41s
test-no-headers	35s
test (ubuntu-latest, 9.0, 0, 1, 0, 0)	2m 2s
test-expectations (macos-latest)	37s
test (ubuntu-latest, 9.0, 0, 1, 1, 0)	1m 48s
test (ubuntu-latest, 9.0, 1, 0, 0, 0)	2m 9s
test (ubuntu-latest, 9.0, 1, 0, 1, 0)	2m 15s
test (ubuntu-latest, 9.0, 1, 1, 0, 0)	2m 18s
test (ubuntu-latest, 9.0, 1, 1, 1, 0)	2m 27s
test (ubuntu-latest, 16.0, 0, 0, 0, 0)	4m 5s
test (ubuntu-latest, 16.0, 0, 0, 1, 0)	4m 31s
test (ubuntu-latest, 16.0, 0, 1, 0, 0)	4m 14s
test (ubuntu-latest, 16.0, 0, 1, 1, 0)	4m 17s
test (ubuntu-latest, 16.0, 1, 0, 0, 0)	4m 51s
test (ubuntu-latest, 16.0, 1, 0, 1, 0)	5m 2s
test (ubuntu-latest, 16.0, 1, 1, 0, 0)	5m 6s
test (ubuntu-latest, 16.0, 1, 1, 1, 0)	5m 40s
test (ubuntu-latest, 16.0, 0, 0, 1)	2m 29s
test (macos-latest, 16.0, 0, 0, 0)	3m 17s
success	1s
	1h 4m 53s

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