Temporarily reverting buildx support

I need to push a container for 0.57 using this action, and I'm not ready to ship other architecture builds until we have tested them in #1344.

.github/workflows/push_docker_tag.yml

@@ -11,31 +11,15 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
-
-    - name: Set up QEMU
-      uses: docker/setup-qemu-action@v1
-
-    - name: Set up Docker Buildx
-      id: buildx
-      uses: docker/setup-buildx-action@v1
-
-    - name: Available platforms
-      run: echo ${{ steps.buildx.outputs.platforms }}
-
-    - name: Login to DockerHub
-      uses: docker/login-action@v1
-      with:
-        username: ${{ secrets.DOCKER_USER }}
-        password: ${{ secrets.DOCKER_PASS }}
-
     - name: Build and push to Docker Hub
-      run: |
-        docker buildx build \
-          --file Dockerfile . \
-          --tag $REPO:${VERSION_TAG} \
-          --build-arg VERSION=${VERSION_TAG} \
-          --platform linux/386,linux/amd64,linux/arm/v6,linux/arm/v7,linux/arm64,linux/ppc64le,linux/s390x \
-          --push
       env:
-        REPO: datasetteproject/datasette
+        DOCKER_USER: ${{ secrets.DOCKER_USER }}
+        DOCKER_PASS: ${{ secrets.DOCKER_PASS }}
         VERSION_TAG: ${{ github.event.inputs.version_tag }}
+      run: |-
+        docker login -u $DOCKER_USER -p $DOCKER_PASS
+        export REPO=datasetteproject/datasette
+        docker build -f Dockerfile \
+          -t $REPO:${VERSION_TAG} \
+          --build-arg VERSION=${VERSION_TAG} .
+        docker push $REPO:${VERSION_TAG}