Fix clippy warnings #542

Job	Run time
Bitrot check	1m 35s
Build target wasm32-unknown-unknown	2m 8s
Book tests	1m 48s
Build target wasm32-wasi	2m 6s
Code coverage	3h 4m 37s
Intra-doc links	1m 54s
Rustfmt	19s
Test on ubuntu-latest	11m 3s
Test on i686-unknown-linux-gnu	22m 50s
Test on windows-latest	14m 54s
Test on i686-unknown-linux-gnu with beta features	22m 3s
Test on macOS-latest	9m 14s
Test on i686-unknown-linux-gnu with nightly features	23m 42s
Test on ubuntu-latest with beta features	11m 4s
Test on windows-latest with beta features	14m 28s
Test on macOS-latest with beta features	8m 47s
Test on ubuntu-latest with nightly features	11m 20s
Test on windows-latest with nightly features	14m 51s
Test on macOS-latest with nightly features	8m 54s
	6h 7m 37s

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