Remove now irrelevant workflow (#235)

.github/workflows/build-push-template.yml

@@ -1,19 +0,0 @@
-name: Build and Push template
-
-on:
-  push:
-    branches:
-    - master
-
-jobs:
-  build-push-template:
-    if: ${{ github.repository == 'substrate-developer-hub/substrate-node-template' }}
-    runs-on: ubuntu-18.04
-    steps:
-    - name: Trigger playground inclusion
-      uses: peter-evans/repository-dispatch@v1
-      with:
-        token: ${{ secrets.REPO_ACCESS_TOKEN }}
-        repository: paritytech/substrate-playground
-        event-type: template-updated
-        client-payload: '{"id": "node-template"}'