[v3] Drop legacy search endpoint

[psrok1]

Your checklist for this pull request

• [x] I've read the contributing guideline.
• [x] I've tested my changes by building and running the project, and testing changed functionality (if applicable)
• [ ] I've added automated tests for my change (if applicable, optional)
• [ ] I've updated documentation to reflect my change (if applicable)

What is the current behaviour?

See #304 (Use GET /api/object?query= instead of POST /api/search)

What is the new behaviour?

This PR removes legacy POST /search endpoint

Minimum supported mwdblib version: https://github.com/CERT-Polska/mwdblib/releases/tag/v3.3.0