mmctl: don't add an update script

The `mattermost` or `mattermostLatest` update scripts handle this.

pkgs/by-name/mm/mmctl/package.nix

@@ -1,12 +1,16 @@
 {
+  lib,
   mattermost,
 }:
 
-mattermost.withoutTests.server.overrideAttrs (o: {
+mattermost.withoutTests.server.overrideAttrs (prev: {
   pname = "mmctl";
   subPackages = [ "cmd/mmctl" ];
 
-  meta = o.meta // {
+  # `mattermost` or `mattermostLatest` handle it
+  passthru = lib.removeAttrs prev.passthru [ "updateScript" ];
+
+  meta = prev.meta // {
     description = "Remote CLI tool for Mattermost";
     mainProgram = "mmctl";
   };