This helps make the Zulip development environment somewhat more robust
to new contributors, since it will give them a nice warning if they
try running any of our development tools outside the Zulip virtualenv.
Fixes#3468.
Previously, we didn't install/pin our own node.js version, and thus
had this wrapper script to manage it. Now that install our own node
via nvm, there's no reason we still need this.
Fixes#2409.