TinyMCE: Remove dashicon-no-alt.png, unused since [30694].

merges [31073] to 4.1 branch.

props kpdesign, MattyRob.
fixes #30791.


Built from https://develop.svn.wordpress.org/branches/4.1@31088


git-svn-id: http://core.svn.wordpress.org/branches/4.1@31069 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/update-core.php

@@ -694,6 +694,7 @@ $_old_files = array(
 'wp-includes/js/jquery/ui/jquery.ui.tabs.min.js',
 'wp-includes/js/jquery/ui/jquery.ui.tooltip.min.js',
 'wp-includes/js/jquery/ui/jquery.ui.widget.min.js',
+'wp-includes/js/tinymce/skins/wordpress/images/dashicon-no-alt.png',
 );
 
 /**