Check that withdrawal credentials in deposit_data.json match those provided in "Generate Keys" step

[petertdavies]

The "Generate Keys" step asks the user to provide a withdrawal address and then adjusts the key generation instructions accordingly. I intentionally provided a valid deposit_data.json with a different withdrawal address to the one used in the "Generate Keys" step.

Doing this should produce at least a warning as it suggests that the user has potentially screwed up their deposit data generation.