workflows: don't build privnet image

It only differs from non-privnet by tag, it doesn't make sense rebuilding the
same things over and over again.

.github/workflows/build.yml

@@ -114,33 +114,3 @@ jobs:
 
       - name: Build Docker image
         run: make image
-
-  build_privnet_image:
-    needs: build_cli
-    name: Build privnet Docker image
-    runs-on: ${{matrix.os}}
-    strategy:
-      matrix:
-        os: [ubuntu-20.04, windows-2022]
-
-    steps:
-      - uses: actions/checkout@v2
-        with:
-          ref: ${{ github.event.inputs.ref }}
-          fetch-depth: 0
-
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v2
-
-      # For proper `deps` make target execution.
-      - name: Set up Go
-        uses: actions/setup-go@v2
-        with:
-          go-version: 1.18
-
-      # For information purposes.
-      - name: Print Docker version
-        run: docker --version
-
-      - name: Build privnet Docker image
-        run: make env_image