docs: remove deleted treap

[alexandear]

This PR removes perdata/treap because it was deleted from GitHub.

$ curl https://api.github.com/repos/perdata/treap
{
  "message": "Not Found",
  "documentation_url": "https://docs.github.com/rest/repos/repos#get-a-repository",
  "status": "404"
}

The package was added in #2457

Summary by CodeRabbit

• Documentation
  • Removed the "treap" package entry from the "Trees" section in the Data Structures and Algorithms list in the README.

[phanirithvij]

Thank you