Remove: deserialize method in favor of pydantic.parse_obj()

[lwasser]

closes #358

Description

This removes the deserialize method and replaces calls to is with pydantic.parse_obj. It also cleans up the tests accordingly.

Type of change

Select the statement best describes this pull request.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update
• [ ] This is a documentation update
• [ ] This is a infrastructure update (docs, ci, etc)
• [x] Other (please describe) this is a deprecation / removal of deprecated features.

Does your PR include tests

If you are fixing a bug or adding a feature, we appreciate (but do not require) tests to support whatever fix of feature you're implementing.

• [x] Yes no NEW tests but i cleaned up the tests accordingly
• [ ] No, i'd like some help with tests
• [ ] This change doesn't require tests

Did you include your contribution to the change log?

• [x] Yes, changelog.md is up-to-date.