INT 2F - PC-DOS Econet v1.05 - REMOVE EVENT HANDLER                             
	AX = C504h
	DS:DX -> event handler
Return: AX = return code (see #03037)
Note:	the interrupt-enable state will be preserved, but interrupts may be
	  enabled during processing of this function
SeeAlso: AX=C500h,AX=C503h,AX=C506h,AX=C508h