[css-display] Don't export 'element'; now that Bikeshed is used outsi…

…de CSS this can cause confusing linking conflicts. #680

css-display/Overview.bs

@@ -25,7 +25,7 @@ Introduction</h2>
 
 	<p><em>This section is normative.</em>
 
-	CSS takes a source document, organized as a tree of <dfn lt="element|element tree" export>elements</dfn>,
+	CSS takes a source document, organized as a tree of <dfn lt="element|element tree">elements</dfn>,
 	and renders it onto a <a href="https://www.w3.org/TR/CSS2/intro.html#canvas">canvas</a> (such as your screen, a piece of paper, or an audio stream).
 	To do this, it generates an intermediary structure,
 	the <dfn export>box tree</dfn>,