Build/Test Tools: Update CSS files after grunt precommit:css.

This removes instances of the `-moz-user-select` property, which was required until Firefox 68.

Firefox is currently in version 84, so these can safely be removed.

Fixes #52332.
Built from https://develop.svn.wordpress.org/trunk@49991


git-svn-id: http://core.svn.wordpress.org/trunk@49692 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/widgets-rtl.css

@@ -38,7 +38,6 @@
 	white-space: nowrap;
 	text-overflow: ellipsis;
 	-webkit-user-select: none;
-	-moz-user-select: none;
 	-ms-user-select: none;
 	user-select: none;
 }
@@ -568,7 +567,6 @@ div#widgets-right .closed .widgets-sortables {
 .widgets-holder-wrap .sidebar-name,
 .widgets-holder-wrap .sidebar-description {
 	-webkit-user-select: none;
-	-moz-user-select: none;
 	-ms-user-select: none;
 	user-select: none;
 }