Using Wizard.exclude_steps applies to all sites in a multisite cluster.
In order to exclude steps for individual sites at run-time, a new
instance method `remove_step` is being added.
It's very easy to forget to add `require 'rails_helper'` at the top of every core/plugin spec file, and omissions can cause some very confusing/sporadic errors.
By setting this flag in `.rspec`, we can remove the need for `require 'rails_helper'` entirely.