Rust

Remove `extern crate` #317

Job	Run time
check	13s
test-linux (i686-unknown-linux-gnu)	35s
test-macos	10s
check-stub	6s
test-linux (i686-unknown-linux-musl)	28s
test-msrv	42s
test-linux (x86_64-unknown-linux-gnu)	16s
test-linux (x86_64-unknown-linux-musl)	16s
test-win (i686-pc-windows-gnu)	43s
test-linux (x86_64-linux-android)	21s
test-win (i686-pc-windows-msvc)	31s
test-win (x86_64-pc-windows-gnu)	41s
test-win (x86_64-pc-windows-msvc)	1m 29s
	6m 31s

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