It can be done - if you have the ServiceNow Data Flows integration and specifically if you wrote from BigFix-to-ServiceNow the BigFix ComputerID, it should be very easy to accomplish. If you do NOT, then what you need it is a two-API call process where first will need to establish the BigFix ComputerID and the second will perform the actual removal (mark as delete).
That said, here is the documented resource you need - DELETE api/computer/{computer id}.