Reset rom settings when formatting flash drive during update

[bvl1999]

When updating firmware, the updater asks if the flash drive should be formatted.

This is problematic when the UII+ or U64 is configured to use alternative kernal or alternative drive roms, or a cartridge, as those files will be gone after a format.

Also, as the default answer to this question is 'yes', this is likely to happen quite often by accident, so I suggest 2 changes:

• ensure the default answer to this question is 'no', unless there was no flash drive before the update.
• when the flash drive is formatted, either reset all settings to their default, or at the very least reset alternate kernal and drive roms to their defaults and disable the configured cartridge.