removed useless workflow

.github/workflows/deploy-theme.yml

@@ -1,15 +0,0 @@
-name: Deploy Theme
-on:
-  push:
-    branches:
-      - master
-jobs:
-  deploy:
-    runs-on: ubuntu-18.04
-    steps:
-      - uses: actions/checkout@v2
-      - name: Deploy Ghost Theme
-        uses: TryGhost/action-deploy-theme@v1.4.0
-        with:
-          api-url: ${{ secrets.GHOST_ADMIN_API_URL }}
-          api-key: ${{ secrets.GHOST_ADMIN_API_KEY }}