Update free-books.md

Author: ericdouglas

extras/free-books.md

@@ -77,7 +77,6 @@ Name | Author(s)
 [Grinstead and Snell’s Introduction to Probability](https://math.dartmouth.edu/~prob/prob/prob.pdf) |Charles M. Grinstead, J. Laurie Snell
 
 ### Computer Architecture
-[The Elements of Computer Systems - From NAND to Tetris](http://www.nand2tetris.org/course.php) |Noam Nisan, Shimon Schocken
 
 ### Operating Systems
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