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/dashboard/polls_spec.rb

@@ -155,7 +155,7 @@ describe "Polls" do
     within ".js-questions" do
       expect(page).to have_css ".nested-fields", count: 2
       within first(".nested-fields") do
-        find("a.delete").click
+        click_link class: "delete"
       end
       expect(page).to have_css ".nested-fields", count: 1
     end
@@ -177,7 +177,7 @@ describe "Polls" do
     within ".js-questions .js-answers" do
       expect(page).to have_css ".nested-fields", count: 2
       within first(".nested-fields") do
-        find("a.delete").click
+        click_link class: "delete"
       end
       expect(page).to have_css ".nested-fields", count: 1
     end