Refine link in build_convert.md for including and using models in programs
Covered by https://github.com/tensorflow/tensorflow/pull/62242
This commit updates the file reference in build_convert.md, replacing the non-existent evaluate.cc link with hello_world_test.cc. The change is reflected in the commit history, as shown in the attached screenshot:

<img width="893" alt="Screen Shot 2023-12-05 at 11 38 21 AM" src="https://github.com/tensorflow/tensorflow/assets/106297042/4ae031a2-0b64-4189-8368-597fb47a9d36">
