brltty: move defaults to package file, use ALSA on Linux

pkgs/tools/misc/brltty/default.nix

···
-{ stdenv, fetchurl, pkgconfig, python3, alsaSupport, alsaLib ? null, bluez, systemdSupport, systemd ? null }:
+{ stdenv, fetchurl, pkgconfig, python3, bluez
+, alsaSupport ? stdenv.isLinux, alsaLib ? null
+, systemdSupport ? stdenv.isLinux, systemd ? null }:
 
 assert alsaSupport -> alsaLib != null;
 assert systemdSupport -> systemd != null;

pkgs/top-level/all-packages.nix

···
 
   brigand = callPackage ../development/libraries/brigand { };
 
-  brltty = callPackage ../tools/misc/brltty {
-    alsaSupport = (!stdenv.isDarwin);
-    systemdSupport = stdenv.isLinux;
-  };
+  brltty = callPackage ../tools/misc/brltty { };
+
   bro = callPackage ../applications/networking/ids/bro { };
 
   bruteforce-luks = callPackage ../tools/security/bruteforce-luks { };