chore: code cleanup

common/net/bufconn.go

@@ -56,8 +56,5 @@ func (c *BufferedConn) ReadBuffer(buffer *buf.Buffer) (err error) {
 }
 
 func (c *BufferedConn) Upstream() any {
-	if wrapper, ok := c.ExtendedConn.(*ExtendedConnWrapper); ok {
-		return wrapper.Conn
-	}
 	return c.ExtendedConn
 }

common/net/sing.go

@@ -8,8 +8,6 @@ import (
 	"github.com/sagernet/sing/common/network"
 )
 
-type ExtendedConnWrapper = bufio.ExtendedConnWrapper
-
 var NewExtendedConn = bufio.NewExtendedConn
 var NewExtendedWriter = bufio.NewExtendedWriter
 var NewExtendedReader = bufio.NewExtendedReader