alttab: Remove sgraf as maintainer

I'm no longer using `alttab` and have no way to test it. That said, maintenance overhead is quite manageable, for anyone interested in picking up.

pkgs/tools/X11/alttab/default.nix

@@ -52,6 +52,6 @@ stdenv.mkDerivation rec {
     description = "X11 window switcher designed for minimalistic window managers or standalone X11 session";
     license = licenses.gpl3Plus;
     platforms = platforms.all;
-    maintainers = [ maintainers.sgraf ];
+    maintainers = [ ];
   };
 }