remove stray http3 connection file

This was accidentally commited in #3411.

http3/conn.go

@@ -1,21 +0,0 @@
-package http3
-
-import "github.com/lucas-clemente/quic-go"
-
-type ConnState struct {
-	SupportsDatagram bool
-}
-
-type Conn struct {
-	conn quic.Connection
-
-	supportsDatagram bool
-}
-
-func (c *Conn) State() ConnState {
-	return ConnState{SupportsDatagram: c.supportsDatagram}
-}
-
-func (c *Conn) SendDatagram(b []byte) error {
-	return c.conn.SendMessage(b)
-}