deps: Remove unused `open` dependency. #328

Job	Run time
cargo fmt	11s
cargo doc (windows-latest)	3m 33s
cargo clippy + test (windows-latest)	6m 8s
cargo doc (macos-latest)	1m 37s
cargo clippy + test (macos-latest)	2m 49s
cargo doc (ubuntu-latest)	1m 58s
cargo clippy + test (ubuntu-latest)	3m 41s
	19m 57s

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