crypto/tls: remove version check when unmarshaling sessionState

This was causing issues when fuzzing with
TestMarshalUnmarshal since the test would
occassionally set the version to VersionTLS13,
which would fail when unmarshaling. The check
doesn't add much in practice, and there is no
harm in removing it to de-flake the test.

Fixes #38902

Change-Id: I0906c570e9ed69c85fdd2c15f1b52f9e372c62e3
Reviewed-on: https://go-review.googlesource.com/c/go/+/234486


Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>