Remove .travis.yml

This does not appear to be used anymore was added with https://gitlab.com/gitlab-org/gitlab-qa/-/commit/95141b328a6015ea51b94e00c792b3c9d1669e0b which was related to packaging and publishing the gitlab-qa gem which is now handled by https://gitlab.com/gitlab-org/quality/pipeline-common/-/blob/master/ci/gem-release.yml now