maintainers: drop x3ro

Inactive since 2022, not part of the GitHub org.

maintainers/maintainer-list.nix

···
     github = "x123";
     githubId = 5481629;
   };
-  x3ro = {
-    name = "^x3ro";
-    email = "[e-mail]";
-    github = "x3rAx";
-    githubId = 2268851;
-  };
   x807x = {
     name = "x807x";
     email = "[e-mail]";

pkgs/by-name/ks/ksnip/package.nix

···
       - Many configuration options.
     '';
     license = lib.licenses.gpl2Plus;
-    maintainers = with lib.maintainers; [ x3ro ];
     platforms = lib.platforms.linux;
     mainProgram = "ksnip";
   };

pkgs/by-name/li/linux-router/package.nix

···
     '';
     changelog = "https://github.com/garywill/linux-router/releases/tag/${version}";
     license = lib.licenses.lgpl21Only;
-    maintainers = with lib.maintainers; [ x3ro ];
     platforms = lib.platforms.linux;
     mainProgram = "lnxrouter";
   };