signal-desktop: deprecate commandLineArgs override

Changing default program arguments should be done via wrappers, not
build time overrides.

Signed-off-by: Marcin Serwin <marcin@serwin.dev>

pkgs/by-name/si/signal-desktop/package.nix

@@ -23,6 +23,9 @@
 
   withAppleEmojis ? false,
 }:
+assert lib.warnIf (commandLineArgs != "")
+  "`commandLineArgs` has been deprecated and will be removed in the future. Consider creating a wrapper script or a desktop entry with your desired flags."
+  true;
 let
   nodejs = nodejs_24;
   pnpm = pnpm_10_29_2;