Remove new-db-field-with-default from migration tests.

[smk4664]

Environment

• cookiecutter-nautobot-app version: 2.4.0

Proposed Functionality

The rule is no longer relevant with the minimum version of Postgres being 12. This rule also cannot be disabled by using the pylint: disable=new-db-field-with-default inline.

pylint-dev/pylint-django#296
https://docs.djangoproject.com/en/3.0/topics/migrations/#postgresql ( I am purposefully going to older docs as the Django 4.2 docs don't even mention it).