signal-desktop: Transfer maintainership

I was actively maintaining the package but stopped using it since the
Ozone/Wayland support broke (e06082eda0 - and I was already migrating
away from Signal anyway).

Mic92 kindly offered to take over and equirosa also offered to become
active again. So it should be in good hands :)
And thank you ixmatus for packaging Signal-Desktop in Nixpkgs.

pkgs/applications/networking/instant-messengers/signal-desktop/default.nix

@@ -147,7 +147,7 @@ in stdenv.mkDerivation rec {
     homepage    = "https://signal.org/";
     changelog   = "https://github.com/signalapp/Signal-Desktop/releases/tag/v${version}";
     license     = lib.licenses.agpl3Only;
-    maintainers = with lib.maintainers; [ ixmatus primeos equirosa ];
+    maintainers = with lib.maintainers; [ mic92 equirosa ];
     platforms   = [ "x86_64-linux" ];
   };
 }