How to remove wires from doorbell
If the electric doorbell(s) are no longer required, there is two steps. First, you need to disconnect the ends of the wires in question from the doorbell transformer. Cut them away from the transformer so no one will be able to reconnect them easily.  Doorbells work on 12 to 28VDC, so the source of voltage should be removed.  Once you are sure there is no electric power on the wires, simply cut them off or stuff them back into the hole, never to be used again. I always clip off any bare copper and fold and tape them so no conductors can come in contact with each other when stuffed in the wall.  Even though it is low voltage, shorting the hot and ground can cause sparks which could be a fire hazard.