Remove legacy code (#3838)

* Add feature migration notice

* Remove legacy code of transport processing

* Clear legacy proto field

* Fix missing

* Unify protocolname

* Test remove

* Supressor

* Weird code

* Remove errorgen related comments

app/observatory/burst/burst.go

@@ -5,8 +5,6 @@ import (
 	"time"
 )
 
-//go:generate go run github.com/v2fly/v2ray-core/v4/common/errors/errorgen
-
 const (
 	rttFailed = time.Duration(math.MaxInt64 - iota)
 	rttUntested