Remove unused overlay value snapshots

overlay.go

@@ -10,8 +10,6 @@ import (
 type overlayRecord struct {
 	change    Change
 	displaced []displacedDefinition
-	before    *document.Node
-	after     *document.Node
 }
 
 type displacedDefinition struct {
@@ -73,7 +71,6 @@ func mergeOverlayMappings(result *composedDocument, target, overlay *document.No
 					Previous: previousOrigins(previous),
 				},
 				displaced: displaced,
-				before:    document.Clone(existing), after: document.Clone(incoming.Value),
 			})
 		}
 	}
@@ -161,8 +158,6 @@ func cloneOverlayRecords(records []overlayRecord) []overlayRecord {
 	cloned := make([]overlayRecord, len(records))
 	for index, record := range records {
 		cloned[index].change = cloneChange(record.change)
-		cloned[index].before = document.Clone(record.before)
-		cloned[index].after = document.Clone(record.after)
 		cloned[index].displaced = make([]displacedDefinition, len(record.displaced))
 		for displacedIndex, displaced := range record.displaced {
 			cloned[index].displaced[displacedIndex] = displacedDefinition{