Remove Unnecessary PhantomData

[bhgomes]

Description

This PR removes unnecessary PhantomData in some structures. See the following:

• GroupAffine, GroupProjective (ec/src/models/short_weierstrass_jacobian.rs)
• GroupAffine, GroupProjective, MontgomeryGroupAffine (ec/src/models/twisted_edwards_extended.rs)
• CubicExtField (ff/src/fields/models/cubic_extension.rs)
• QuadExtField (ff/src/fields/models/quadratic_extension.rs)

The rest of the changes are cargo clippy or cargo fmt updates.

---

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (master)
• Linked to Github issue with discussion and accepted design OR have an explanation in the PR that describes this work.
• (N/A) Wrote unit tests
• (N/A) Updated relevant documentation in the code
• Added a relevant changelog entry to the Pending section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

[weikengchen]

Hi, Brandon, I just fixed the linter issue of the master branch and is ready to merge many PRs in the next a few days.

One question: can you change this PR into "Allow edits by maintainers"? If it is right, it would be somewhere on the right of this page.
https://docs.github.com/en/github/collaborating-with-pull-requests/working-with-forks/allowing-changes-to-a-pull-request-branch-created-from-a-fork

I will then sync with the master branch and perform final cleanup if necessary.

[bhgomes]

On this pull request, it doesn't show "Allow edits by maintainers", probably because the pull request comes from an organization-fork rather than from me directly. I didn't know that this would happen if I used an organization. Next time, I'll use my own fork, but in the meantime, you can send me a diff, or I can re-fork it to my own account if you like. Sorry about the inconvenience!

[weikengchen]

This is a very nice improvement of the existing code.