Revert "Fix background color of Notification in chameleon theme (#14246)"

This reverts commit 13eb3732b9.

WebContent/VAADIN/themes/chameleon/components/notification/notification.scss

@@ -8,9 +8,6 @@ div.#{$primaryStyleName} {
 	-webkit-box-shadow: 0 2px 5px rgba(0,0,0,.7);
 	-moz-box-shadow: 0 2px 5px rgba(0,0,0,.7);
 	box-shadow: 0 2px 5px rgba(0,0,0,.7);
-	//IE8 does not support rgba, using just rgb
-	background:rgb(255,255,255) url(../img/grad-light-top.png) repeat-x;
-	background:rgba(255,255,255,.90) url(../img/grad-light-top.png) repeat-x;
 	}
 
 .#{$primaryStyleName} p {