Revert "DOPS-602: Change how mmctl gets packaged and locally fetched. (#18335)" (#18930)

This reverts commit 5ede63badc.

scripts/mmctl-dev.sh

@@ -1,20 +0,0 @@
-#!/usr/bin/env bash
-set -xe
-
-if [[ "$(basename "$PWD")" != "mattermost-server" ]]; then
-  echo "please run this script from the root project folder of mattermost-server with ./scripts/mmctl-dev.sh"
-  exit 1
-fi
-
-if [ ! -d "../mmctl" ]; then
-  echo "please clone mmctl as a companion repository on the same level next to mattermost-server (git@github.com:mattermost/mmctl.git)"
-  exit 1
-fi
-
-cd ../mmctl
-make build
-cd -
-
-cp ../mmctl/mmctl bin/mmctl
-
-./bin/mmctl version