feat: Remove gitlab-ci yml file (#25782)

.gitlab-ci.yml

@@ -1,22 +0,0 @@
-stages:
-  - test
-  - build
-  - publish
-  - create-vars
-  - trigger-build-ee
-
-include:
-  - project: mattermost/ci/mattermost-server
-    ref: master
-    file: private.yml
-
-variables:
-  BUILD: "yes"
-  IMAGE_BUILD_SERVER: $CI_REGISTRY/mattermost/ci/images/mattermost-build-server:20230904_golang-1.20.7
-  IMAGE_BUILD_DOCKER: $CI_REGISTRY/mattermost/ci/devops-images/mattermost-build-docker:23.0.1-0
-  IMAGE_DIND: $CI_REGISTRY/mattermost/ci/devops-images/docker-dind:23.0.1-0
-
-empty:
-  stage: create-vars
-  script:
-    - echo "empty"