Administration: Hide skip to toolbar link on small viewports.

Since r55326, the admin sidebar autocloses on small viewports when focus exits the sidebar. Because of this, there is no case where the Skip to Toolbar link will have any function on small viewports.

Props sabernhardt, abcd95, alh0319, mleray, joedolson.
Fixes #63286.

git-svn-id: https://develop.svn.wordpress.org/trunk@60286 602fd350-edb4-49c9-b593-d223f7449a82

Author: joedolson

src/wp-admin/css/common.css

@@ -3912,6 +3912,10 @@ img {
 		top: 7px;
 	}
 
+	.screen-reader-shortcut[href="#wp-toolbar"] {
+		display: none;
+	}
+
 	body {
 		min-width: 240px;
 		overflow-x: hidden;