Extract poll question option images from shared nested imageable specs to system specs

This is the only it_behaves_like "nested imageable" call where the has_many_images parameter is set to true.

Previously, the shared example skipped or altered expectations based on this parameter. Now, this behavior is
moved to the factory level (:future_poll_question_option).

Since this is an administrative section, a related administrator is created for the user.

spec/system/admin/poll/questions/options/images/images_spec.rb

@@ -4,15 +4,6 @@ describe "Images", :admin do
   let(:future_poll) { create(:poll, :future) }
   let(:current_poll) { create(:poll) }
 
-  it_behaves_like "nested imageable",
-                  "future_poll_question_option",
-                  "new_admin_option_image_path",
-                  { option_id: "id" },
-                  nil,
-                  "Save image",
-                  "Image uploaded successfully",
-                  true
-
   context "Index" do
     scenario "Option with no images" do
       option = create(:poll_question_option)