remove unused import

proxy/dokodemo/sockopt_linux.go

@@ -8,7 +8,6 @@ import (
 	"github.com/v2ray/v2ray-core/common/log"
 	v2net "github.com/v2ray/v2ray-core/common/net"
 	"github.com/v2ray/v2ray-core/transport/internet"
-	"github.com/v2ray/v2ray-core/transport/internet/tcp"
 )
 
 const SO_ORIGINAL_DST = 80