go/types, types2: don't print aliased type (in comments) for Alias types

go/types, types2: don't print aliased type (in comments) for Alias types

Fixes #64584.

Change-Id: I756d6026d10f130c1dd5026891b7cc3c640d7f78
Reviewed-on: https://go-review.googlesource.com/c/go/+/548135
Reviewed-by: Alan Donovan <adonovan@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>