Remove Github Actions configuration, migrated to Buildbot

.github/workflows/build-image.yml

@@ -1,24 +0,0 @@
-name: Docker image build
-
-on:
-  push:
-    branches:
-      - master
-
-jobs:
-  build:
-    runs-on: ubuntu-latest
-
-    steps:
-    - uses: actions/checkout@v2
-    - name: Build the Docker image
-      run: >-
-        docker build . \
-          --file docker/Dockerfile \
-          --build-arg=BUILD_SERIES=dev \
-          --build-arg=BUILD_ID="$(echo "$GITHUB_SHA" | head -c 12)" \
-          --tag snikket/snikket:dev
-    - name: Log into registry
-      run: echo "${{ secrets.DOCKER_HUB_ACCESS_TOKEN }}" | docker login -u snikket --password-stdin
-    - name: Push the Docker image
-      run: docker push snikket/snikket:dev

.github/workflows/build-release-image.yml

@@ -1,32 +0,0 @@
----
-name: Docker release image build
-
-"on":
-  push:
-    tags:
-      - release/*.*
-
-jobs:
-  build:
-    runs-on: ubuntu-latest
-
-    steps:
-      - uses: actions/checkout@v2
-      - name: Build the Docker image
-        run: >-
-          echo "Building ref $GITHUB_REF...";
-          RELEASE_TAG="${GITHUB_REF#refs/tags/release/}";
-          RELEASE_SERIES="${RELEASE_TAG%.*}";
-          RELEASE_VER="${RELEASE_TAG#$RELEASE_SERIES.}";
-          docker build . \
-            --file docker/Dockerfile \
-            --build-arg=BUILD_SERIES="$RELEASE_SERIES" \
-            --build-arg=BUILD_ID="$RELEASE_VER" \
-            --tag snikket/snikket:"$RELEASE_SERIES"
-      - name: Log into registry
-        run: echo "${{ secrets.DOCKER_HUB_ACCESS_TOKEN }}" | docker login -u snikket --password-stdin
-      - name: Push the Docker image
-        run: >-
-          RELEASE_TAG="${GITHUB_REF#refs/tags/release/}";
-          RELEASE_SERIES="${RELEASE_TAG%.*}";
-          docker push snikket/snikket:"$RELEASE_SERIES"