crypto/tls: remove return parameter stutter
crypto/tls: remove return parameter stutter

Per https://golang.org/s/style#named-result-parameters

Change-Id: If69d3e6d3dbef385a0f41e743fa49c25475ca40c
Reviewed-on: https://go-review.googlesource.com/2761
Reviewed-by: Adam Langley <db68fba232b2c49ed3e9d3081df349dde7b61dfd@golang.org>

Jigsaw-Code/utls