go/types: fix incorrect comment at Info.Implicits.

Change-Id: Ibd24e1567cb03f7f00f3cbe381bedd6c5215af35
Reviewed-on: https://go-review.googlesource.com/15320Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/types/api.go

@@ -142,7 +142,7 @@ type Info struct {
 	//
 	//	*ast.ImportSpec    *PkgName for dot-imports and imports without renames
 	//	*ast.CaseClause    type-specific *Var for each type switch case clause (incl. default)
-	//      *ast.Field         anonymous struct field or parameter *Var
+	//      *ast.Field         anonymous parameter *Var
 	//
 	Implicits map[ast.Node]Object