Switching from str to UUID, max_length creates issues in generated code

[henriklindgren]

Reproduce by setting up a str attribute

switching it to UUID without removing max_length

Results in:
Required(UUID, 255, unique=True, default=uuid4). causing TypeError: Unexpected positional argument for attribute Model.some_id: 255

Fixable by moving back to str and removing offending field, or editing manually.