Hardening: Remove the ability to upload JavaScript files for users who do not have the `unfiltered_html` capability.

Merges [42261] to the 4.8 branch.

Built from https://develop.svn.wordpress.org/branches/4.8@42271


git-svn-id: http://core.svn.wordpress.org/branches/4.8@42100 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/functions.php

@@ -2553,8 +2553,9 @@ function get_allowed_mime_types( $user = null ) {
 	if ( function_exists( 'current_user_can' ) )
 		$unfiltered = $user ? user_can( $user, 'unfiltered_html' ) : current_user_can( 'unfiltered_html' );
 
-	if ( empty( $unfiltered ) )
-		unset( $t['htm|html'] );
+	if ( empty( $unfiltered ) ) {
+		unset( $t['htm|html'], $t['js'] );
+	}
 
 	/**
 	 * Filters list of allowed mime types and file extensions.