Remove all redundant link CSS

Giving all links the GOVUK Frontend classes, and
the new `govuk-link--destructive` class, means
some styles are already applied.

This strips out those styles.

Note: there's still a good amount of styling, most
of which is to make the focus styles specific to
the space the link is in. These will need
reviewing when GOVUK Frontend is bumped past
version 3 as this brings in new focus styles.

app/assets/stylesheets/views/notification.scss

@@ -6,18 +6,14 @@
 
   &.error {
 
-    color: $error-colour;
+    color: $govuk-error-colour;
     font-weight: bold;
 
-    a {
-      color: $error-colour;
-    }
-
   }
 
   &-cancelled {
     @include bold-19;
-    color: $error-colour;
+    color: $govuk-error-colour;
   }
 
 }