Remove old, unused heroku-toolbelt PATH addition [heroku]
Fix my custom zsh binstubs problem with different rubies

When dealing with different rubies, the script would incorrectly set
$GEM_HOME to "default" rvm ruby for projects not using bundler.

This custom $GEM_HOME "restoring" functionality is now removed so that
rvm can deal with $GEM_HOME for us.

Seems to work.