Revert "Tweak code and docs for Broccoli Env support"

This reverts commit fac6d810692aa4cfae4710bae0f43e2b8368fd15.
Revert "Add support for broccoli environment variable"

This reverts commit 3b0febdcd0ebe975af1d625125c077603e437c7e.

Conflicts:
	package.json
Updated for Broccoli 0.12.x and removed `env` support

Fixes #4