Remove Sparc GNU plugin.

[Rot127]

Your checklist for this pull request

• [x] I've read the guidelines for contributing to this repository.
• [x] I made sure to follow the project's coding style.
• [ ] I've documented every RZ_API function and struct this PR changes.
• [ ] I've added tests that prove my changes are effective (required for changes to RZ_API).
• [ ] I've updated the Rizin book with the relevant information (if needed).

Detailed description

Simple removal

Test plan

All green

Closing issues

Ticks a box in https://github.com/rizinorg/rizin/issues/2704