renice: remove unused import in test #52

Job	Run time
cargo fmt --all -- --check	4s
cargo check (ubuntu-latest)	8s
cargo clippy -- -D warnings (ubuntu-latest)	10s
cargo check (macOS-latest)	24s
cargo clippy -- -D warnings (macOS-latest)	21s
Code Coverage (ubuntu-latest, unix)	1m 24s
cargo check (windows-latest)	1m 19s
cargo test (ubuntu-latest)	18s
cargo clippy -- -D warnings (windows-latest)	1m 23s
Code Coverage (macos-latest, macos)	1m 22s
cargo test (macOS-latest)	1m 22s
Code Coverage (windows-latest, windows)	1m 2s
cargo test (windows-latest)	1m 25s
	10m 42s

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