Removing and deprecating the old Dockerfile.

The eext docker image is now served by barney docker registry.
This avoids specifying the image contents in both Dockerfile and
Barneyfile. Now, we have an unified view.
BDR Image:
barney-docker.infra.corp.arista.io/code.arista.io/eos/tools/eext-bus
See https://github.com/aristanetworks/eext-bus/blob/main/README.md
for detailed instructions.

.github/workflows/eext-lint.yaml

@@ -14,14 +14,6 @@ jobs:
 
     steps:
       - uses: actions/checkout@v3
-      - name: Lint Dockerfile
-        uses: hadolint/[email protected]
-        with:
-          # using recursive to avoid hardcoding paths
-          # and missing any future additions
-          recursive: true
-          verbose: true
-          ignore: DL3002
 
       - name: Lint yaml files
         run: yamllint .