ci: remove GitLab sync workflow as it's no longer needed

.github/workflows/sync-gitlab.yml

@@ -1,25 +0,0 @@
-name: Sync to GitLab
-
-permissions:
-  contents: read
-
-on:
-  push:
-  workflow_dispatch:
-
-jobs:
-  sync:
-    runs-on: ubuntu-latest
-    steps:
-    - name: Checkout repository
-      uses: actions/checkout@v4
-      with:
-        fetch-depth: 0
-
-    - name: Sync to GitLab
-      uses: keninkujovic/gitlab-sync@2.1.0
-      with:
-        gitlab_url: https://gitlab.com/TheWildJames/${{ github.event.repository.name }}.git
-        username: TheWildJames
-        gitlab_pat: ${{ secrets.GITLAB_PAT }}
-        force_push: true