install.sh: update to match main repo

ci/travis/install.sh

@@ -1,11 +0,0 @@
-#!/usr/bin/env bash
-#
-# install.sh
-#
-# This file is meant to be sourced during the `install` phase of the Travis
-# build. Do not attempt to source or run it locally.
-#
-# shellcheck disable=SC1090
-. "${TRAVIS_BUILD_DIR}/ci/travis/helpers.sh"
-
-header 'Running install.sh...'