Remove Sandbox repository link from README

Removed outdated link to the Sandbox repository in README.

Author: bbzaffari

README.md

@@ -25,7 +25,6 @@ Designed for maximum performance and scalability, it integrates vector search, O
 │   ├── build/               # Generated build files
 │   ├── Conanfile.py         # Package manager for C and C++
 │   └── CMakeLists.txt       # Main build config
-├── <a href="https://github.com/bbzaffari/purecpp/blob/main/Sandbox/README.md#sandbox-repository">Sandbox/</a>     
 ├── models/                  
 │   ├── hf_extract_model.py
 │   ├── hf_model_to_onnx.py