Omit first_name and last_name in User model

[Andrew-Chen-Wang]

Description

Fixes #1268

Remove first_name and last_name from User model. This is just how I personally did it awhile ago.

Checklist:

• I've made sure that tests/test_cookiecutter_generation.py is updated accordingly (especially if adding or updating a template option)
• I've updated the documentation or confirm that my change doesn't require any updates

Rationale

We already have a name attribute, and the other attributes aren't used in any forms (as far as I can see in my current project).

[browniebroke]

Thanks again @Andrew-Chen-Wang !