Remove binstubs!

The soon-to-be-released Rails 4 no longer plays nice with `bundle install --binstubs`. Bundler-managed binstubs are now discouraged. So I'm removing them from source control. Each developer can choose how to solve the `bundle exec` problem (I chose to use https://github.com/mpapis/rubygems-bundler).

More information on Rails 4 vs Bundler here: https://github.com/bundler/bundler/issues/2253