remove log format type check

Option `LogConfig` is omitempty in config.
That means we allow `c.HostConfig.LogConfig` is nil. There is no
need to check the log type, we don't use it now in log sub
command, maybe in the furture.

cli/logs.go

@@ -68,10 +68,6 @@ func (lc *LogsCommand) runLogs(args []string) error {
 		return err
 	}
 
-	if !validDrivers[c.HostConfig.LogConfig.Type] {
-		return fmt.Errorf("\"logs\" command is supported only for \"json-file\" and \"journald\" logging drivers (got; %s)", c.HostConfig.LogConfig.Type)
-	}
-
 	opts := types.ContainerLogsOptions{
 		ShowStdout: true,
 		ShowStderr: true,