Remove duplicate OSTEP entry

Author: Anshul-Patidar

books/free-programming-books-subjects.md

@@ -791,6 +791,8 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [Making Servers Work: A Practical Guide to Linux System Administration](https://www.digitalocean.com/community/books/sysadmin-ebook-making-servers-work) - Jamon Camisso (PDF, EPUB)
 * [Operating Systems: From 0 to 1](https://github.com/tuhdo/os01/releases/tag/0.0.1) - Tu, Ho Doang (PDF) ( :construction: *in process*)
 * [Operating Systems: Three Easy Pieces](https://pages.cs.wisc.edu/~remzi/OSTEP/) - Remzi H. Arpaci-Dusseau and Andrea C. Arpaci-Dusseau (PDF)
+* [Operating Systems: Three Easy Pieces](https://pages.cs.wisc.edu/~remzi/OSTEP/)
+
 * [Practical File System Design: The Be File System](https://www.nobius.org/~dbg/practical-file-system-design.pdf) - Dominic Giampaolo (PDF)
 * [Project Oberon: The Design of an Operating System, a Compiler, and a Computer](https://people.inf.ethz.ch/wirth/ProjectOberon/index.html) - Niklaus Wirth, Jürg Gutknecht (PDF)
 * [The Art of Unix Programming](http://catb.org/esr/writings/taoup/html/) - Eric S. Raymond (HTML)
@@ -800,7 +802,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [UNIX Application and System Programming, lecture notes](http://www.compsci.hunter.cuny.edu/~sweiss/course_materials/unix_lecture_notes.php) - Stewart Weiss (PDF) (CC BY-SA)
 * [Writing a Simple Operating System from Scratch](https://www.cs.bham.ac.uk/~exr/lectures/opsys/10_11/lectures/os-dev.pdf) - Nick Blundell (PDF)
 * [Xv6, a simple Unix-like teaching operating system](https://pdos.csail.mit.edu/6.828/2022/xv6.html) - Russ Cox, Frans Kaashoek and Robert Morris (PDF, HTML)
-* [Operating Systems: Three Easy Pieces](https://pages.cs.wisc.edu/~remzi/OSTEP/)
+