encoding/openapi: simplify looping over CUE fields

Including definitions in the iterator, only to then skip over them,
seems unnecessary.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I0e660ef63394026f4e1781cf5dfbd88556955a7b
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1204946
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
Reviewed-by: Roger Peppe <rogpeppe@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>

encoding/openapi/openapi.go

@@ -145,10 +145,7 @@ func (c *Config) compose(inst cue.InstanceOrValue, schemas *ast.StructLit) (x *a
 	var title, version string
 	var info *ast.StructLit
 
-	for i, _ := val.Fields(cue.Definitions(true)); i.Next(); {
-		if i.Selector().IsDefinition() {
-			continue
-		}
+	for i, _ := val.Fields(); i.Next(); {
 		label := i.Selector().Unquoted()
 		attr := i.Value().Attribute("openapi")
 		if s, _ := attr.String(0); s != "" {