Remove missed code path for api < 1.12

Signed-off-by: Antonio Murdaca <runcom@linux.com>

api/server/server.go

@@ -1124,7 +1124,6 @@ func (s *Server) postContainersAttach(version version.Version, w http.ResponseWr
 		UseStderr: boolValue(r, "stderr"),
 		Logs:      boolValue(r, "logs"),
 		Stream:    boolValue(r, "stream"),
-		Multiplex: version.GreaterThanOrEqualTo("1.6"),
 	}
 
 	if err := s.daemon.ContainerAttachWithLogs(vars["name"], attachWithLogsConfig); err != nil {

daemon/attach.go

@@ -11,7 +11,6 @@ type ContainerAttachWithLogsConfig struct {
 	OutStream                      io.Writer
 	UseStdin, UseStdout, UseStderr bool
 	Logs, Stream                   bool
-	Multiplex                      bool
 }
 
 func (daemon *Daemon) ContainerAttachWithLogs(name string, c *ContainerAttachWithLogsConfig) error {
@@ -22,7 +21,7 @@ func (daemon *Daemon) ContainerAttachWithLogs(name string, c *ContainerAttachWit
 
 	var errStream io.Writer
 
-	if !container.Config.Tty && c.Multiplex {
+	if !container.Config.Tty {
 		errStream = stdcopy.NewStdWriter(c.OutStream, stdcopy.Stderr)
 		c.OutStream = stdcopy.NewStdWriter(c.OutStream, stdcopy.Stdout)
 	} else {