crypto/tls: revert "add HandshakeContext method to Conn"

crypto/tls: revert "add HandshakeContext method to Conn"

This reverts CL 246338.

Reason for revert: waiting for 1.17 release cycle

Updates #32406

Change-Id: I074379039041e086c62271d689b4b7f442281663
Reviewed-on: https://go-review.googlesource.com/c/go/+/269697
Run-TryBot: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>
Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
Trust: Katie Hockman <katie@golang.org>
Trust: Roland Shoemaker <roland@golang.org>