Ensure namespaced class is findable

We get occasional uninitialized constant exceptions because the
Whitehall::ExtraQuoteRemover class cannot be found. This adds the class to its
parent module such that it can be found regardless of the execution path
of the code. See http://urbanautomaton.com/blog/2013/08/27/rails-autoloading-hell/
for more details about constant lookup and Rails autoload.
Explicitly require dependencies

Rails autoloading cannot be relied upon to load nested classes, particularly
when the code is being executed in a background job. Better to be explicit about
the dependencies.
Ensure GovUkDelivery code is correctly loaded.

As with the previous two commits, we cannot always guarantee namespaced modules
and classes will get correctly loaded in sidekiq jobs. This should ensure that
the GovUkDelivery classes can be found.
Remove unused and unnecessary code

Two of these modules were not being used and the other one is redundant as the
methods within it are only being used in one place.