Remove NIOS-II architecture

[XVilka]

Your checklist for this pull request

• I've read the guidelines for contributing to this repository
• I made sure to follow the project's coding style
• I've documented or updated the documentation of every function and struct this PR changes. If not so I've explained why.
• I've added tests that prove my fix is effective or that my feature works (if possible)
• I've updated the rizin book with the relevant information (if needed)

Detailed description

• It was untested and unused (not a single bug was reported in 10+ years)
• It is a software architecture for use in FPGA, too niche and rarely used for firmware RE
• It is deprecated by Linux kernel, GCC, QEMU, and so on: https://lore.kernel.org/qemu-devel/[email protected]/

Test plan

CI is green

Closing issues

Partially addresses #2704

[pelijah]

You forgot to update README and labeler config