Remove global link styles

All links, that need it, now have the GOVUK
Frontend link class so we no longer need this
CSS.

app/assets/stylesheets/app.scss

@@ -1,10 +1,4 @@
 // Extra CSS overlaying elements
-a {
-  &:visited {
-    color: $link-colour;
-  }
-}
-
 .form-control-1-1 {
   width: 100%;
 }