Removing the post install script for the gulp branch.

Per https://github.com/roots/roots/issues/1212
yeah I know haha. "which installs front-end packages defined in `bower.json`." this is needed because devs will be actively modifying the bower.json. I don't want anyone to get confused and think that they need to be working with bower *and* package.json

"This installs all the tools needed for the build process." that is much less confusing.

@retlehs