Convert ReceiveAsync to Receive

[Aaronontheweb]

eliminates unnecessary delegate allocation under the covers.

[marcinbudny]

Hi @Aaronontheweb, thank you for this contribution.

These are the new numbers:

Clients: 750
Before:  207450 req/s
After:   197344 req/s

Which is ~ -4.9% drop. So the throughput is slightly lower. I ran the benchmark two times with both versions and the drop was similar in both cases. There is of course the issue of reproducibility, because this runs on public cloud, so the environment is not fully controlled and isolated. So maybe that might have an effect as well.

Let me know if you want me to merge this change.