Remove async-lock #477

Job	Run time
rust_ci (macos-latest, stable)	1m 43s
rust_ci (macos-latest, beta)	1m 4s
rust_ci (macos-latest, nightly)	1m 46s
rust_ci (ubuntu-latest, stable)	1m 9s
rust_ci (ubuntu-latest, beta)	1m 5s
rust_ci (ubuntu-latest, nightly)	1m 47s
rust_ci (windows-latest, stable)	2m 30s
rust_ci (windows-latest, beta)	1m 49s
rust_ci (windows-latest, nightly)	3m 41s
	16m 34s

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