memcpy operations break on queue with lazy_queue property

[Bensuo]

Trying to do a memcpy using a queue with the lazy_queue property causes program termination with the following error:

die: The host-visible proxy event missing
terminate called without an active exception

This presents an issue for both example code/test having to manually initialize USM memory and also for future users of a prototype implementation who would likely want to use memcpy.

[EwanC]

lazy queue property has been removed by #100 so closing issue.