chore: Remove not needed travis configuration

.travis.yml

-language: bash
-
-env:
-  - BUILDX_VERSION=0.4.2 DOCKER_VERSION=test
-  - BUILDX_VERSION=0.4.2 DOCKER_VERSION=stable
-  - BUILDX_VERSION=0.4.2 DOCKER_VERSION=19.03
-  - BUILDX_VERSION=0.4.1 DOCKER_VERSION=test
-  - BUILDX_VERSION=0.4.1 DOCKER_VERSION=stable
-  - BUILDX_VERSION=0.4.1 DOCKER_VERSION=19.03
-  - BUILDX_VERSION=0.4.0 DOCKER_VERSION=test
-  - BUILDX_VERSION=0.4.0 DOCKER_VERSION=stable
-  - BUILDX_VERSION=0.4.0 DOCKER_VERSION=19.03
-  - BUILDX_VERSION=0.3.1 DOCKER_VERSION=test
-  - BUILDX_VERSION=0.3.1 DOCKER_VERSION=stable
-  - BUILDX_VERSION=0.3.1 DOCKER_VERSION=19.03
-
-services:
-  - docker
-
-branches:
-  only:
-    - master
-
-script:
-  - docker build --build-arg BUILDX_VERSION=$BUILDX_VERSION --build-arg DOCKER_VERSION=$DOCKER_VERSION -t jdrouet/docker-with-buildx:$DOCKER_VERSION-$BUILDX_VERSION .
-  - echo "$DOCKER_PASSWORD" | docker login -u "$DOCKER_USERNAME" --password-stdin
-  - docker push jdrouet/docker-with-buildx:$DOCKER_VERSION-$BUILDX_VERSION