Int 15 Fn 18  - Multidos Plus - Unmap Irq                                  [T]

   AH = 18h
   AL = IRQ to unmap (01h-0Fh)

Return: AX = status
       0000h successful
       0001h invalid IRQ

Note:  results are unpredictable if the IRQ has not been mapped

See Also: AH=17h"MultiDOS",AH=19h"MultiDOS"