Remove redundant feature settings enabled in tests

These settings are enabled by default.

It could be argued explicitely enabling the features makes tests more
consistent, because they'll work if we change the default setting. It
could also be argued that it makes tests more expressive because it
makes the reader realize certain things will only work if a setting is
enabled.

However, we were only doing so in a few tests. The truth is, thousands
of our tests depend on certain features being enabled. So IMHO we should
be consistent and either set them on every test, or not at all. I'm
choosing the latter option for simplicity.

spec/shared/features/nested_imageable.rb

@@ -9,9 +9,6 @@ shared_examples "nested imageable" do |imageable_factory_name, path, imageable_p
   let!(:imageable)           { create(imageable_factory_name) }
 
   before do
-
-    Setting["feature.allow_images"] = true
-
     imageable_path_arguments&.each do |argument_name, path_to_value|
       arguments.merge!("#{argument_name}": imageable.send(path_to_value))
     end