go/ast: fix Object's doc comment about Data

The doc comment about the Data field of go/ast.Object reflects its old
behavior, from when the go/types typechecker depended on ast.Objects.

Since when the doc was written, the behavior has changed in
https://golang.org/cl/7058060 and https://golang.org/cl/7096048 .

Fixes #18631

Change-Id: I10fc3e31cfbf7b303eec44150df917f6eb285f90
Reviewed-on: https://go-review.googlesource.com/35075Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/ast/scope.go

@@ -70,10 +70,8 @@ func (s *Scope) String() string {
 // The Data fields contains object-specific data:
 //
 //	Kind    Data type         Data value
-//	Pkg	*types.Package    package scope
+//	Pkg     *Scope            package scope
 //	Con     int               iota for the respective declaration
-//	Con     != nil            constant value
-//	Typ     *Scope            (used as method scope during type checking - transient)
 //
 type Object struct {
 	Kind ObjKind