travis: don't overwrite amd64 images with arm64

.travis.yml

@@ -39,22 +39,6 @@ jobs:
       script:
         - go run build/ci.go docker -upload karalabe/geth-docker-test
 
-    # This builder does the Docker Hub build and upload for arm64
-    - stage: build
-      if: type = push
-      os: linux
-      arch: arm64
-      dist: bionic
-      go: 1.16.x
-      env:
-        - docker
-      services:
-        - docker
-      git:
-        submodules: false # avoid cloning ethereum/tests
-      script:
-        - go run build/ci.go docker -upload karalabe/geth-docker-test
-
     # This builder does the Ubuntu PPA upload
     - stage: build
       if: type = push