Remove unused dependencies: greenlet, cffi

[gdrosos]

Summary

This pull request addresses the removal of the unused dependencies greenlet and cffi from the project. It's part of an ongoing research endeavor focusing on the identification and elimination of code bloat within software projects.

Rationale

The greenlet dependency was added in 180a65e but remains unused, serving only as a transitive dependency. Similarly, the cffi dependency, added in 2208815, is no longer required due to updates in the cryptography dependencies.

Removing these unused dependencies contributes to a leaner codebase, reduces security risks, and simplifies dependency management.

Changes

• Removed greenlet and cffi dependencies from requirements.in.
• Updated requirements3.txt to reflect the removed dependencies.

Impact

• Decreased package size
• Enhanced project maintainability

I also signed the Contributor License Agreement (CLA) according to the contributing guidelines

[gdrosos]

Hello @ramonpetgrave64, @skiptomyliu, @alejandroroiz

I hope this message finds you well. We are currently engaged in a research project focused on optimizing projects by identifying and eliminating unnecessary dependencies. Your insights and expertise as a maintainer would greatly contribute to our research efforts.

Could you please take a moment to review these changes? Your input would be highly valuable to us.

Thank you for your consideration!