remove useless docker build in CI (#746)

Author: MarinPostma

.github/workflows/rust.yml

@@ -109,21 +109,3 @@ jobs:
     - name: Test openssl
       shell: bash {0}
       run: cargo tree -p sqld -i openssl; [ $? = 101 ]
-
-  docker:
-    runs-on: ubuntu-latest
-    name: Build Docker
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v3
-        with:
-          submodules: recursive
-      - name: Set up QEMU
-        uses: docker/setup-qemu-action@v2
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v2
-      - name: Build
-        uses: docker/build-push-action@v3
-        with:
-          context: .
-          tags: sqld:unstable