Use Capybara methods to find/click/check links

We applied the Capybara/SpecificMatcher in commit f52a86b46.  However,
this rule doesn't convert methods finding <a> tags to methods finding
links because <a> tags only count as links when they've got the `href`
attribute. For instance, in the `xss_spec.rb` file we check what happens
when clicking on an anchor tag because we're testing that the `href`
attribute has been removed and so we can't use `click_link`.

So, basically, we can't enable a rule to automatically detect when we're
using `have_css` instead of `have_link`, but we should still do it
because `have_link` adds an extra check which affects accessibility
since it makes sure the tag has the `href` attribute and so it's
recognizable as a link by screen readers.

spec/shared/system/nested_imageable.rb

@@ -228,7 +228,7 @@ shared_examples "nested imageable" do |imageable_factory_name, path, imageable_p
         click_link "Remove image"
 
         expect(page).not_to have_css ".image"
-        expect(page).to have_css "a#new_image_link"
+        expect(page).to have_link id: "new_image_link"
       end
 
       scenario "don't duplicate fields after removing and adding an image" do