go/types, types2: simplify TestUnaliasTooSoonInCycle (cleanup)

go/types, types2: simplify TestUnaliasTooSoonInCycle (cleanup)

Follow-up on CL 576975 and CL 579015.

Updates #66704
Updates #65294

Change-Id: Ied95386a346be38ccda86d332d09b2089a68c5e7
Reviewed-on: https://go-review.googlesource.com/c/go/+/579075
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>