Remove reference to private slides repo

Author: ShuhaoZhangTony

README.md

@@ -27,6 +27,5 @@ The lecture slides live in a separate repository (PDF + LaTeX). This repo is int
 
 - Primary slides PDF (GitHub Pages): [https://intellistream.github.io/parallel-computing-course-java-demos/main.pdf](https://intellistream.github.io/parallel-computing-course-java-demos/main.pdf)
 - Slides landing page: [https://intellistream.github.io/parallel-computing-course-java-demos/](https://intellistream.github.io/parallel-computing-course-java-demos/)
-- Slides source repo (may be private): [https://github.com/intellistream/parallel-computing-course-java](https://github.com/intellistream/parallel-computing-course-java)
 
 Note: the `gh-pages` branch of this repository is auto-generated by CI from the slides source repo.