triedb/hashdb: Avoid setting db.cleans on Close (#29309)

triedb/hashdb/database.go

@@ -619,7 +619,6 @@ func (db *Database) Size() (common.StorageSize, common.StorageSize) {
 func (db *Database) Close() error {
 	if db.cleans != nil {
 		db.cleans.Reset()
-		db.cleans = nil
 	}
 	return nil
 }