go/types, types2: replace 2 uses of Scope.LookupParent with Checker.lookup
A step towards removing reliance on Scope.LookupParent.
Updates #69673.
Change-Id: I9fdd4b08ea600b531b90895ac779fdc580ff00e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/616259
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Auto-Submit: Robert Griesemer <gri@google.com>
Commit-Queue: Robert Griesemer <gri@google.com> Reviewed-by: Robert Griesemer <gri@google.com> Reviewed-by: Alan Donovan <adonovan@google.com>