Remove unnecessary require_dependency

  This was causing a load error inside watermarkresources:

  ~/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/activesupport-5.1.5/lib/active_support/concern.rb:126:in `included': Cannot define multiple 'included' blocks for a Concern (ActiveSupport::Concern::MultipleIncludedBlocks)
	from ~/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/bundler/gems/wcc-contentful-f0b98a0f473a/wcc-contentful/lib/wcc/contentful/event.rb:33:in `<module:Event>'
	from ~/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/bundler/gems/wcc-contentful-f0b98a0f473a/wcc-contentful/lib/wcc/contentful/event.rb:3:in `<top (required)>'
	from ~/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/activesupport-5.1.5/lib/active_support/dependencies.rb:477:in `load'

wcc-contentful/app/controllers/wcc/contentful/webhook_controller.rb

@@ -1,8 +1,6 @@
 # frozen_string_literal: true
 
 require_dependency 'wcc/contentful/application_controller'
-require_dependency 'wcc/contentful/event'
-require 'wisper'
 
 module WCC::Contentful
   # The WebhookController is mounted by the WCC::Contentful::Engine to receive