crypto/tls: remove typeNextProtocol

crypto/tls: remove typeNextProtocol

Was this strictly necessary? No.
Did this deserve its own CL? Maybe not.
But I have a personal vendetta against NPN.

Change-Id: Ide1ad1092259dc23e3ead5c1d5269fc5cb2793d7
Reviewed-on: https://go-review.googlesource.com/c/go/+/587275
Reviewed-by: Roland Shoemaker <roland@golang.org>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>