CSS: Remove use of getDefaultComputedStyle

Remove optimization to make jQuery compatible with Google's Polymer project

Closes gh-1647
Fixes #15227

src/css/defaultDisplay.js

@@ -13,19 +13,9 @@ var iframe,
  */
 // Called only from within defaultDisplay
 function actualDisplay( name, doc ) {
-	var style,
-		elem = jQuery( doc.createElement( name ) ).appendTo( doc.body ),
+	var elem = jQuery( doc.createElement( name ) ).appendTo( doc.body ),
 
-		// getDefaultComputedStyle might be reliably used only on attached element
-		display = window.getDefaultComputedStyle &&
-			( style = window.getDefaultComputedStyle( elem[ 0 ] ) ) ?
-
-				// Use of this method is a temporary fix (more like optimization)
-				// until something better comes along,
-				// since it was removed from specification and supported only in FF
-				style.display :
-
-				jQuery.css( elem[ 0 ], "display" );
+		display = jQuery.css( elem[ 0 ], "display" );
 
 	// We don't have any data stored on the element,
 	// so use "detach" method as fast way to get rid of the element