Remove small redundancy in prose

Author: frivoal

css-overflow-3/Overview.bs

@@ -175,7 +175,7 @@ Scrollable overflow</h3>
 			Issue: Need to evaluate compat of honoring or ignoring 'clip' and 'clip-path'.
 	</ul>
 
-	Additionally, the UA may <em>additionally</em> include
+	The UA may <em>additionally</em> include
 	the margin areas of boxes for which it is the containing block.
 	The conditions under which such margin areas are included is undefined in this level.
 	<span class="issue">This needs further testing and investigation; is therefore deferred in this draft.</span>