trie: update the `valid` function comments (#29809)

trie/sync.go

@@ -157,7 +157,7 @@ type nodeOp struct {
 	hash  common.Hash // hash of the node content (empty for node deletion)
 }
 
-// isDelete indicates if the operation is a database deletion.
+// valid checks whether the node operation is valid.
 func (op *nodeOp) valid() bool {
 	if op.del && len(op.blob) != 0 {
 		return false