.gitlab-ci.yml: Remove unnecessary SSH auth

We're using token-based auth now, using a project access token.

.gitlab-ci.yml

@@ -56,14 +56,12 @@ pages:
 ci:merge:
     stage: deploy
     script:
-        - eval $(ssh-agent -s)
-        - ssh-add <(echo "$SSH_PRIVATE_KEY")
         - git config user.email "gitlab-ci@localhost"
         - git config user.name "GitLab CI"
         - git checkout main
         - git reset --hard origin/main
         - git merge --ff origin/stage
-        # Should trigger pipeline
+        # This will trigger main pipeline after pushing
         - git push http://ci:$STAGE_MERGE_ACCESS_TOKEN@$CI_SERVER_HOST/$CI_PROJECT_PATH.git HEAD:main
     only:
         - stage