the block heater typically replaced one of the core plugs in the block. It had a heating element in the new plug, that a short cable connects to and runs to the center grill area. From there, Ford supplied a cord that plugs into this, and then into your extension cord.
so to delete the block heater, you can locate the engine bay cord and remove it from the freeze plug.
removing the heater from the block is a different story as it requires draining the coolant, pulling the core plug, and installing a new plug.