sage.rings.finite_rings.element_*: Remove unused imports

[mkoeppe]

Likewise for the module providing the parent class.

Also replace an import that is more specific than necessary, which helps for modularization.

• Part of: Meta-ticket: Modularize sagelib into separate distributions (pip-installable packages) sagemath-... for Sage 10.x #29705
• Cherry-picked from: Modularization of sagelib: Distributions sagemath-{brial,combinat,eclib,flint,gap,giac,glpk,graphs,groups,homfly,lcalc,libbraiding,libecm,linbox,modules,mpmath,ntl,pari,plot,polyhedra,schemes,singular,standard-no-symbolics,symbolics} #35095

📝 Checklist

• The title is concise, informative, and self-explanatory.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation accordingly.

⌛ Dependencies

[dcoudert]

You could do the same in sage/rings/finite_rings/element_givaro.pyx.

[github-actions]

Documentation preview for this PR (built with commit c0bad32; changes) is ready! 🎉

[dcoudert]

LGTM.

[mkoeppe]

Thank you!