`armv7-unknown-linux-musleabihf`/`armv7-linux-musleabihf` hard-coded NEON support

[briansmith]

See https://github.com/rust-embedded/cross/blob/718a19cd68fb09428532d1317515fe7303692b47/docker/armv7-unknown-linux-musleabihf/Dockerfile#L30

According to rust-lang/rust#47765 this is wrong.

See also rust-lang/rust#56947 where new NEON-always-available target triples were added.

[jamesmunns]

Hey @briansmith, would you mind please removing this in a PR? I can kick off CI once you submit it.