Test attachments from the user's point of view

These tests were checking the URLs of documents and images pointed to
the URL generated by the `attachment.url` method. In order to do so, we
were running database queries after starting the process running the
browser, which is sometimes causing database inconsistencies when
running the tests.

So I'm simply removing the URL check. The tests are slightly less useful
now, but it isn't like they were 100% right in the first place. After
all, if the `attachment.url` method wasn't working properly, the tests
were still passing.

spec/system/admin/site_customization/documents_spec.rb

@@ -58,7 +58,7 @@ describe "Documents", :admin do
     click_button "Upload"
 
     expect(page).to have_content "Document uploaded succesfully"
-    expect(page).to have_link "logo.pdf", href: Document.last.attachment.url
+    expect(page).to have_link "logo.pdf"
   end
 
   scenario "Errors on create" do

spec/system/admin/widgets/cards_spec.rb

@@ -40,19 +40,18 @@ describe "Cards", :admin do
   end
 
   scenario "Index" do
-    3.times { create(:widget_card) }
+    cards = Array.new(3) { create(:widget_card) }
 
     visit admin_homepage_path
 
     expect(page).to have_css(".homepage-card", count: 3)
 
-    cards = Widget::Card.all
     cards.each do |card|
       expect(page).to have_content card.title
       expect(page).to have_content card.description
       expect(page).to have_content card.link_text
       expect(page).to have_content card.link_url
-      expect(page).to have_link("Show image", href: card.image_url(:large))
+      expect(page).to have_link "Show image"
     end
   end