crypto/x509: drop compatibility hack for expired COMODO intermediates

The hack was there for a couple intermediates with only SGC EKUs that
issued severAuth certificates. They now all expired, so we can drop it.

https://crt.sh/?id=10066
https://crt.sh/?id=213

Change-Id: I46820024892b2f9918ce125bafbbaf9e6c5c58b3
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/781225
Reviewed-on: https://go-review.googlesource.com/c/go/+/327809


Trust: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>