Remove Docker BuildX Action.

Its too slow

.github/workflows/buildimage.yml

@@ -1,31 +0,0 @@
-name: buildx
-
-on:
-  push:
-    branches: mqtt
-
-jobs:
-  buildx:
-    runs-on: ubuntu-latest
-    steps:
-      -
-        name: Checkout
-        uses: actions/checkout@v1
-        with:
-          ref: mqtt
-      -
-        name: Set up Docker Buildx
-        id: buildx
-        uses: crazy-max/ghaction-docker-buildx@v1
-        with:
-          version: latest
-      -
-        name: Available platforms
-        run: echo ${{ steps.buildx.outputs.platforms }}
-      -
-        name: Run Buildx
-        run: |
-          docker buildx build \
-            --platform linux/amd64,linux/arm/v7,linux/arm64 \
-            --output "type=image,push=false" \
-            --file ./Docker/Dockerfile .