http2: remove the timeout since we don't know a good value
http2: remove the timeout since we don't know a good value

The test is expected to finish so rather than wait on some arbitrary
timeout, let the go test timeout show us where things went wrong.

Fixes golang/go#42381

Change-Id: Ia9405f9f75b2f5f73ed3f8a540a74b7c64066ad0
Reviewed-on: https://go-review.googlesource.com/c/net/+/267977
Run-TryBot: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Trust: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

golang/net