Issue#2 deleteasync

No performance gain...

```
### DELETING RECORDS

* deleting native mongodb documents x 692 ops/sec ±3.73% (70 runs sampled)
* deleting mongoose documents x 443 ops/sec ±1.82% (81 runs sampled)
* deleting neo4j nodes x 153 ops/sec ±20.82% (63 runs sampled)
* deleting mongraph documents x 97.69 ops/sec ±10.57% (58 runs sampled)
* deleting mongraph documents + nodes async x 66.36 ops/sec ±1.82% (80 runs sampled)

**Fastest** is deleting native mongodb documents

**Slowest** is deleting mongraph documents + nodes async
```