supersonic-wayland: drop darwin as supported platform

Wayland support is only possible on Linux. Instead of the assert, which
can't be caught by CI properly, do this via the list of supported
platforms in `meta.platforms`. This works much better for CI.

pkgs/by-name/su/supersonic/package.nix

@@ -16,8 +16,6 @@
   waylandSupport ? false,
 }:
 
-assert waylandSupport -> stdenv.hostPlatform.isLinux;
-
 buildGoModule rec {
   pname = "supersonic" + lib.optionalString waylandSupport "-wayland";
   version = "0.17.0";
@@ -97,7 +95,7 @@ buildGoModule rec {
     mainProgram = "supersonic" + lib.optionalString waylandSupport "-wayland";
     description = "Lightweight cross-platform desktop client for Subsonic music servers";
     homepage = "https://github.com/dweymouth/supersonic";
-    platforms = platforms.linux ++ platforms.darwin;
+    platforms = platforms.linux ++ lib.optionals (!waylandSupport) platforms.darwin;
     license = licenses.gpl3Plus;
     maintainers = with maintainers; [
       zane