Merge branch 'ee-10535-buttons-css' into 'master'

EE: Removes EE differences for buttons.scss

See merge request gitlab-org/gitlab-ee!10340

app/assets/stylesheets/framework/buttons.scss

@@ -443,6 +443,7 @@
     border-color: transparent;
   }
 
+  &.btn-secondary-hover-link,
   &.btn-default-hover-link {
     color: $gl-text-color-secondary;