GN_Uab, Unlink an alarm block from the alarm chain

Register parameters

RST 20H, DEFW $6E09
IN:
     BHL = extended pointer of alarm block
OUT, if call successful:
     Fc = 0
     Fz = 1, Alarm block dequeued.
OUT, if call failed:
     Fc = 1
     A = error code:
          RC_BAD ($04), bad arguments

Registers changed after return:
     ..BCDEHL/IXIY same
     AF....../.... different 

Notes

The system only does limited error checking. If the alarm is done, the symbol counter is decremented, and the done flag is reset. If the alarm is pending it is cancelled,

Related calls

GN_Aab, allocate alarm block
GN_Alp, process an expired alarm (internal OZ usage)
GN_Fab, free alarm block
GN_Lab, link an alarm block into the alarm chain
OS_Alm, alarm manipulation (internal OZ usage)