Fix memory leak in RichTextLabel.remove_line

(cherry picked from commit f21b5e4d2fb53e692988e01bf4f5b4957dd9422c)

scene/gui/rich_text_label.cpp

@@ -1667,6 +1667,7 @@ void RichTextLabel::_remove_item(Item *p_item, const int p_line, const int p_sub
 			_remove_item(p_item->subitems.front()->get(), p_line, p_subitem_line);
 		}
 	}
+	memdelete(p_item);
 }
 
 void RichTextLabel::add_image(const Ref<Texture> &p_image, const int p_width, const int p_height) {