)
Call NESL function DeRegisterEventConsumer with:
	BX = 0005h
	ES:SI -> CECB previously passed to RegisterEventConsumer (see #03022)
Return: AX = completion code (0h, 8002h, 8008h) (see #03019)
	ES:SI -> still points to CECB
	BP,DS,STACK preserved
Desc:	Allows a module to de-register as a consumer of a given event class
SeeAlso: #03015,#03017