nubus-device: remove nubus_register_rom() and nubus_register_format_block()

nubus-device: remove nubus_register_rom() and nubus_register_format_block()

Since there is no need to generate a dummy declaration ROM, remove both
nubus_register_rom() and nubus_register_format_block(). These will shortly be
replaced with a mechanism to optionally load a declaration ROM from disk to
allow real images to be used within QEMU.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20210924073808.1041-11-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>