remove defunct links (#3550)

* remove defunct links

* Update free-programming-books.md

free-programming-books.md

@@ -1020,7 +1020,6 @@ Kerridge (PDF) (email address *requested*, not required)
 * [C++ Language](http://www.cplusplus.com/doc/tutorial/)
 * [C++ Notes](https://goalkicker.com/CPlusPlusBook) (PDF)
 * [C++ Succinctly, Syncfusion](https://www.syncfusion.com/resources/techportal/ebooks/cplusplus) (PDF, Kindle) (email address *requested*, not required)
-* [C++ Today](https://www.oreilly.com/ideas/c++-today) - Jon Kalb, Gašper Ažman
 * [C++ Tricks](http://www.bordoon.com/cplusplus/book_wrapper.html)
 * [CS106X Programming Abstractions in C++](http://web.stanford.edu/class/cs106x/)
 * [Elements of Programming](http://elementsofprogramming.com) - Alexander Stepanov and Paul McJones - (PDF)
@@ -1032,7 +1031,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [How To Think Like a Computer Scientist: C++ Version](http://greenteapress.com/thinkcpp/index.html) - Allen B. Downey
 * [Introduction to Design Patterns in C++ with Qt](http://ptgmedia.pearsoncmg.com/images/9780131879058/downloads/0131879057_Ezust_book.pdf) (PDF)
 * [Joint Strike Fighter, C++ Coding Standards, by Bjarne Stroustrup](http://www.stroustrup.com/JSF-AV-rules.pdf) (PDF)
-* [Learn C++.](http://www.learncpp.com) (PDF, Online)
+* [Learn C++.](http://www.learncpp.com) (Online)
 * [Matters Computational: Ideas, Algorithms, Source Code, by Jorg Arndt](http://www.jjj.de/fxt/fxtbook.pdf) (PDF)
 * [Open Data Structures (In C++)](http://opendatastructures.org/ods-cpp.pdf) (PDF)
 * [Software Design Using C++](http://cis.stvincent.edu/html/tutorials/swd/) - Br. David Carlson and Br. Isidore Minerd