Remove the deprecated bytes!() macro

[SimonSapin]

The bytes!() macro is deprecated (see issue #15017) in favor of b"foo" byte literals. It should be removed at some point, preferably before 1.0.

CC @alexcrichton

[steveklabnik]

This has been removed.

[goertzenator]

Can this be brought back as "concat_bytes!" ? Byte literals are great, but the concat part has been lost. My use case is to append a null byte to byte literals at compile-time. bytes! would have been great for that. We have concat! and concat_idents!, so concat_bytes! would seem to make sense.

[SimonSapin]

Yeah, makes sense. The best way to make it happen is probably an RFC backed by a pull request.