remove $? formatting from song format while converting to string

this fixes wrong results while searching for phrase
that contains dollar or one of dollar formatting.

src/settings.h

@@ -158,6 +158,7 @@ struct NcmpcppConfig
 	std::string empty_tag;
 	std::string song_list_columns_format;
 	std::string song_list_format;
+	std::string song_list_format_dollar_free;
 	std::string song_status_format;
 	std::string song_status_format_no_colors;
 	std::string song_window_title_format;