gha: remove docker ci workflow

.github/workflows/push.yml

@@ -1,26 +0,0 @@
-name: Push workflow
-
-on: [push]
-
-jobs:
-  test:
-    runs-on: ubuntu-18.04
-    steps:
-    - uses: actions/checkout@master
-
-    - name: Docker build and print Hugo version
-      env:
-        DOCKER_IMAGE: ${{ github.repository }}:${{ github.sha }}
-      run: |
-        docker build . --file Dockerfile --tag ${DOCKER_IMAGE} &&
-        docker run ${DOCKER_IMAGE} version ||
-        (echo -e "\e[31m[${GITHUB_WORKFLOW}] failed to build\e[m" && exit 1)
-
-  hadolint:
-    runs-on: macOS-10.14
-    steps:
-    - uses: actions/checkout@master
-    - name: hadolint
-      run: |
-        brew install hadolint
-        hadolint ./Dockerfile