style: remove un-styling of dfn, var

Fixes #1919.

assets/stylesheets/global/_base.scss

@@ -96,8 +96,6 @@ dd {
   + dt { margin-top: 1em; }
 }
 
-dfn, var { font-style: normal; }
-
 abbr, acronym, dfn {
   cursor: help;
   border-bottom: 1px dotted var(--textColor);