Remove `killall node` now that webpack-dev-server bug has been fixed

Original discussions here: !252 (closed), !253 (merged)

webpack-dev-server bug fix
https://github.com/webpack/webpack-dev-server/pull/787

.gitlab-ci.yml

@@ -39,8 +39,6 @@ test:install:
     - netstat -lpt
     - gdk install
     - support/set-gitlab-upstream
-    - killall node || true
     - gdk run &
     - sleep 30
     - curl -f --retry 10 --retry-delay 5 http://127.0.0.1:3000/
-