Remove magic-sys/libmagic dependency or something

[JoeOsborn]

It doesn't really work on mac without special cargo flags and hacks. Could use mime-sniffer or mime-guess or something or just not do it

[ekaltman]

This is an issue, as noted in rust magic-sys robo9k/rust-magic-sys#34 . There are undefined symbols in the arm64 libmagic that will block compilation on macOS unless the compiler is set to ignore undefined.