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/system/debates_spec.rb

@@ -19,7 +19,7 @@ describe "Debates" do
       within("#debates") do
         expect(page).to have_content debate.title
         expect(page).to have_content debate.description
-        expect(page).to have_css("a[href='#{debate_path(debate)}']", text: debate.title)
+        expect(page).to have_link debate.title, href: debate_path(debate)
       end
     end
   end