message: don't fetch riot/master by default when installing e2e tests
diff: # run with PUPPETEER_SKIP_CHROMIUM_DOWNLOAD=true sh install.sh if chrome is already installed
  set -e
  ./synapse/install.sh
  -./riot/install.sh
  +# both CI and local testing don't need a riot fetched from master,
  +# so not installing this by default anymore
  +# ./riot/install.sh
  yarn install
  