CICD: Remove Workflow to Build ubuntu 14.04 Docker Image.

Remove the workflow for building an ubuntu 14.04 Docker image. This is
no longer needed since the AppImage is now built on 16.04.

Signed-off-by: Michael Keller <github@ike.ch>

.github/workflows/linux-dockerimage.disabled

@@ -1,39 +0,0 @@
-name: Linux Qt 5.12 Docker Image CI
-
-#on:
-#  push:
-#    paths:
-#    - scripts/docker/trusty-qt512/Dockerfile
-#    - .github/workflows/linux-docker*
-
-jobs:
-  trusty-qt512:
-    runs-on: ubuntu-latest
-    env:
-      VERSION: ${{ '1.0' }}    # 'official' images should have a dot-zero version
-
-    steps:
-    - uses: actions/checkout@v1
-
-    - name: Get our pre-reqs
-      run: |
-        cd scripts/docker/trusty-qt512
-        bash getpackages.sh
-
-    - name: set env
-      run: |
-        v=${{ env.VERSION }}
-        b=${{ github.ref }} # -BRANCH suffix, unless the branch is master
-        b=${b/refs\/heads\//}
-        b=${b,,} # the name needs to be all lower case
-        if [ $b = "master" ] ; then b="" ; else b="-$b" ; fi
-        echo "::set-env name=NAME::subsurface/trusty-qt512${b}:${v}"
-
-    - name: Build and Publish Linux Docker image to Dockerhub
-      uses: elgohr/Publish-Docker-Github-Action@master
-      with:
-        name:       ${{ env.NAME }}
-        username:   ${{ secrets.DOCKER_USERNAME }}
-        password:   ${{ secrets.DOCKER_PASSWORD }}
-        dockerfile: 'Dockerfile'
-        workdir:    './scripts/docker/trusty-qt512/'