Revert "Minor performance improvement"

This reverts commit 33dc8b8.

Author: aimeos

src/Map.php

@@ -4102,14 +4102,8 @@ public function rekey( callable $callback ) : self
 	 */
 	public function remove( $keys ) : self
 	{
-		If( !is_iterable( $keys ) ) {
-			$keys = [$keys];
-		}
-
-		$list = $this->list();
-
-		foreach( (array) $keys as $key ) {
-			unset( $list[$key] );
+		foreach( $this->array( $keys ) as $key ) {
+			unset( $this->list()[$key] );
 		}
 
 		return $this;