Remove outdated RUSTSEC exemption for macOS #304

Job	Run time
cargo-deny (advisories)	19s
cargo-deny (bans licenses sources)	20s
lint	34s
aarch64-apple-darwin / build	55s
aarch64-apple-ios / build	55s
aarch64-unknown-linux-gnu / build	39s
aarch64-unknown-linux-musl / build	47s
arm-linux-androideabi / build	21s
armv7-linux-androideabi / build	26s
i686-pc-windows-gnu / build	1m 41s
i686-pc-windows-msvc / build	1m 20s
i686-unknown-linux-gnu / build	33s
i686-unknown-linux-musl / build	50s
msrv / build	44s
x86_64-apple-darwin / build	51s
x86_64-pc-windows-msvc / build	1m 9s
x86_64-pc-windows-gnu / build	1m 43s
x86_64-unknown-freebsd / build	22s
x86_64-unknown-linux-gnu / build	50s
x86_64-unknown-linux-musl / build	47s
x86_64-unknown-netbsd / build	24s
	16m 30s

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