Remove unused variables

Detected thanks to the RSpec/LetSetup rule after updating rubocop-rspec.

spec/shared/models/acts_as_imageable.rb

@@ -1,6 +1,5 @@
 shared_examples "acts as imageable" do |imageable_factory|
   let!(:image) { build(:image, imageable_factory.to_sym) }
-  let!(:imageable)              { image.imageable }
 
   it "is valid" do
     expect(image).to be_valid

spec/shared/models/document_validations.rb

@@ -2,7 +2,6 @@ shared_examples "document validations" do |documentable_factory|
   include DocumentablesHelper
 
   let!(:document)               { build(:document, documentable_factory.to_sym) }
-  let!(:documentable)           { document.documentable }
   let!(:maxfilesize)            { max_file_size(document.documentable.class) }
   let!(:acceptedcontenttypes)   { accepted_content_types(document.documentable.class) }
 

spec/shared/models/image_validations.rb

@@ -2,7 +2,6 @@ shared_examples "image validations" do |imageable_factory|
   include ImageablesHelper
 
   let!(:image)                  { build(:image, imageable_factory.to_sym) }
-  let!(:imageable)              { image.imageable }
   let!(:acceptedcontenttypes)   { imageable_accepted_content_types }
 
   it "is valid" do

spec/shared/system/followable.rb

@@ -1,7 +1,6 @@
 shared_examples "followable" do |followable_class_name, followable_path, followable_path_arguments|
   let!(:arguments) { {} }
   let!(:followable) { create(followable_class_name) }
-  let!(:followable_dom_name) { followable_class_name.tr("_", "-") }
 
   def dom_id(record)
     ActionView::RecordIdentifier.dom_id(record)

spec/shared/system/imageable.rb

@@ -2,9 +2,7 @@ shared_examples "imageable" do |imageable_factory_name, imageable_path, imageabl
   let!(:administrator)       { create(:user) }
   let!(:user)                { create(:user) }
   let!(:imageable_arguments) { {} }
-  let!(:imageables_arguments)   { {} }
   let!(:imageable)           { create(imageable_factory_name, author: user) }
-  let!(:imageable_dom_name)     { imageable_factory_name.parameterize }
 
   before do
     create(:administrator, user: administrator)