remove broken link in programming books subjects (#10903)

books/free-programming-books-subjects.md

@@ -629,7 +629,6 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [Philosophy of Computer Science](https://www.cse.buffalo.edu/~rapaport/Papers/phics.pdf) (PDF)
 * [PNG: The Definitive Guide](http://www.libpng.org/pub/png/book/) - Greg Roelofs
 * [Pointers And Memory](http://cslibrary.stanford.edu/102/PointersAndMemory.pdf) - Nick Parlante (PDF)
-* [Principles of Computer System Design](http://ocw.mit.edu/resources/res-6-004-principles-of-computer-system-design-an-introduction-spring-2009/online-textbook/part_ii_open_5_0.pdf) (PDF)
 * [Programming Fundamentals](https://press.rebus.community/programmingfundamentals/) - Kenneth Leroy Busbee, Dave Braunschweig
 * [Programming with Unicode](https://unicodebook.readthedocs.org)
 * [Real-World Maintainable Software](https://www.oreilly.com/ideas/real-world-maintainable-software) - Abraham Marin-Perez