scripts: west_commands: runners: nrf_common: adjust json output

Make the generated json file match the contents generated with:
  * nrfutil device erase --uicr --core Application --x-operation-id 1
    --x-family nrf54h --x-append-batch batch.json
  * nrfutil device program --firmware uicr_merged.hex
    --options chip_erase_mode=ERASE_NONE,verify=VERIFY_READ
    --core Application --x-operation-id 2 --x-family nrf54h
    --x-append-batch batch.json
  * nrfutil device reset --reset-kind RESET_PIN --x-operation-id 3
    --x-append-batch batch.json

The erase options are supposed to be placed under "option" subkey.
Without the "option" subkey, nrfutil defaulted to ERASE_ALL.

Remove the firmware file format field because it is auto detected by
nrfutil when executing the batch script.

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>