windows: drop dependency on windows-sys #230

Job	Run time
native-test (nightly, ubuntu-latest)	18s
native-test (nightly, windows-latest)	47s
windows-test (nightly, x86_64-pc-windows-gnu)	1m 1s
cross-ios-build (nightly, aarch64-apple-ios)	16s
native-test (nightly, macOS-latest)	39s
windows-test (nightly, i686-pc-windows-gnu)	59s
bare-cross-build (nightly, x86_64-unknown-haiku)	25s
cross-ios-build (nightly, x86_64-apple-ios)	21s
native-test (stable, ubuntu-latest)	9s
windows-test (stable, x86_64-pc-windows-gnu)	1m 44s
bare-cross-build (nightly, x86_64-unknown-openbsd)	27s
cross-ios-build (stable, aarch64-apple-ios)	9s
native-test (stable, windows-latest)	1m 3s
windows-test (stable, i686-pc-windows-gnu)	1m 18s
bare-cross-build (nightly, x86_64-unknown-redox)	26s
native-test (stable, macOS-latest)	36s
cross-ios-build (stable, x86_64-apple-ios)	11s
bare-cross-build (nightly, x86_64-fuchsia)	26s
native-test (1.56.0, ubuntu-latest)	3m 27s
bare-cross-build (nightly, wasm32-unknown-unknown)	23s
native-test (1.56.0, windows-latest)	4m 18s
native-test (1.56.0, macOS-latest)	7m 10s
	26m 33s

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