net/http: update bundled http2
net/http: update bundled http2

Updates http2 to x/net/http2 git rev c73622c77280

http2: always delay closing the connection after sending GOAWAY
https://golang.org/cl/71372

http2: Discard data reads on HEAD requests
https://golang.org/cl/72551

Fixes #18701
Fixes #22376

Change-Id: I2460cec64848992fff21790868b5fb8c91f050f2
Reviewed-on: https://go-review.googlesource.com/75210
Run-TryBot: Tom Bergan <3b77d7da34779f829901a664ac7c87d255b041af@google.com>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

Cofyc/go,cloudflare/go,cloudflare/go,akutz/go,nawawi/go,akutz/go,josharian/go,cloudflare/go,Cofyc/go,CAFxX/go,nawawi/go,codestation/go,nawawi/go,Cofyc/go,josharian/go,CAFxX/go,cloudflare/go,CAFxX/go,golang/go,Cofyc/go,josharian/go,Cofyc/go,akutz/go,golang/go,codestation/go,cloudflare/go,codestation/go,akutz/go,golang/go,Cofyc/go,nawawi/go,cloudflare/go,CAFxX/go,akutz/go,christopher-henderson/Go,Cofyc/go,golang/go,codestation/go,CAFxX/go,akutz/go,nawawi/go,cloudflare/go,CAFxX/go,josharian/go,josharian/go,codestation/go,codestation/go,akutz/go,CAFxX/go,cloudflare/go,golang/go,codestation/go,josharian/go,josharian/go,nawawi/go,nawawi/go,Cofyc/go,golang/go,nawawi/go,golang/go,josharian/go,akutz/go,CAFxX/go,codestation/go,golang/go