Merge branch 'remove-unnecessary-css' into 'master'

Remove .katex-display from selector

See merge request gitlab-org/gitlab-ce!22580

app/assets/stylesheets/framework/typography.scss

@@ -34,7 +34,7 @@
     margin-bottom: 0;
   }
 
-  *:first-child:not(.katex-display) {
+  *:first-child {
     margin-top: 0;
   }