Clean-up after test_prefix_iterator

tests/test_iterator.rs

@@ -193,6 +193,8 @@ pub fn test_prefix_iterator() {
             assert_eq!(b_iterator.collect::<Vec<_>>(), expected)
         }
     }
+    let opts = Options::default();
+    assert!(DB::destroy(&opts, path).is_ok());
 }
 
 #[test]