http2: remove unused ClientConn.tconnClosed

It was added in CL 429060 but was never used.

Change-Id: Ie1bcd44559006082afed319c0db677ff2ca957d7
Reviewed-on: https://go-review.googlesource.com/c/net/+/523935
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

http2/transport.go

@@ -291,8 +291,7 @@ func (t *Transport) initConnPool() {
 // HTTP/2 server.
 type ClientConn struct {
 	t             *Transport
-	tconn         net.Conn // usually *tls.Conn, except specialized impls
-	tconnClosed   bool
+	tconn         net.Conn             // usually *tls.Conn, except specialized impls
 	tlsState      *tls.ConnectionState // nil only for specialized impls
 	reused        uint32               // whether conn is being reused; atomic
 	singleUse     bool                 // whether being used for a single http.Request