DragonflyBSD: Remove unused Errno's
DragonflyBSD: Remove unused Errno's

EUNUSED* were removed from <sys/errno.h> in DragonflyBSD, so there is no
need for them to be in nix either. This also fixes the build on
DragonflyBSD.

Signed-off-by: Levente Kurusa <855c91457b18bc4d5995dfa202dd377c2433de4a@acm.org>

carllerche/nix-rust,carllerche/nix-rust,geofft/nix-rust,geofft/nix-rust,asomers/nix,geofft/nix-rust,nix-rust/nix,asomers/nix,nix-rust/nix,carllerche/nix-rust