lib.teams: Remove dummy Nixpkgs committers team and hardcode into feature freeze script

There's no reason this needs to be exposed under `lib.teams`

maintainers/scripts/feature-freeze-teams.pl

@@ -75,3 +75,5 @@ while (my ($team_nix_key, $team_config) = each %{$data}) {
 
     print {*STDOUT} "\n";
 }
+
+print {*STDOUT} "Everyone else: \@NixOS/nixpkgs-committers\n";

maintainers/team-list.nix

@@ -418,15 +418,6 @@ with lib.maintainers;
     enableFeatureFreezePing = true;
   };
 
-  # Dummy group for the "everyone else" section
-  feature-freeze-everyone-else = {
-    members = [ ];
-    github = "nixpkgs-committers";
-    scope = "Dummy team for the #everyone else' section during feture freezes, not to be used as package maintainers!";
-    shortName = "Everyone else";
-    enableFeatureFreezePing = true;
-  };
-
   flutter = {
     members = [
       mkg20001