Revert "Enable log feature when using --log-filename"

This reverts commit c3116b2b56.

On second thought, this is less appropriate when using the configuration
file. We may want to define the log filename in config file but not
necessarily enable log feature.

src/options.c

@@ -371,7 +371,6 @@ void options_parse(int argc, char *argv[])
                 break;
 
             case OPT_LOG_FILE:
-                option.log = true;
                 option.log_filename = optarg;
                 break;