Fix various Clippy lints #447

Job	Run time
Clippy	16s
Docs	17s
CheckTargets	1m 9s
Check (armv7-sony-vita-newlibeabihf)	33s
Check (sparcv9-sun-solaris)	31s
MinimalVersions (ubuntu-latest)	22s
MSRV (ubuntu-latest)	1m 26s
Check (x86_64-pc-solaris)	29s
Nightly	21s
MinimalVersions (macos-latest)	22s
MSRV (windows-latest)	2m 5s
MinimalVersions (windows-latest)	46s
Rustfmt	7s
Sanitizer (address)	1m 0s
Test (ubuntu-latest)	50s
Test (macos-latest)	41s
Sanitizer (leak)	48s
TestPoll	30s
Test (windows-latest)	1m 38s
TestWakerPipe	33s
Sanitizer (memory)	1m 42s
Sanitizer (thread)	56s
Passed	0s
	17m 22s

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