Provide better name for validate_email option

[josevalim]

The code also validates if the email changed but I think adding uniqueness to the option is good enough?

[SteffenDE]

Do you have more context about this? Looking at this I find just validate_email fine as is, but I may be missing the problem.

[josevalim]

The issue is that we do other email validations, such as on the format, even when validate_email: false.