audio/spotify-player: Move CARGO_CRATES list to Makefile.crates

Mk/Uses/cargo.mk looks for Makefile.crates in MASTERDIR, so move the
list of CARGO_CRATES there to have a smaller and cleaner Makefile
and to make updates easier with

make cargo-crates > Makefile.crates.

Reported by: eduardo
Approved by: jfree (maintainer)
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D36662