Removed dead links (#5785)

* Updated a broken llink

Updated a broken link to the book "Mastering Xamarin UI Development, Second Edition" by Steven F. Daniel

* Added missing author to title

Added missing author name to the title "Creating Mobile Apps with Xamarin.Forms C#" by Charles Petzold

* Removed dead links

books/free-programming-books-langs.md

@@ -249,13 +249,11 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 
 ### Android
 
-* [Android 4 App Development Essentials](http://www.techotopia.com/index.php/Android_4_App_Development_Essentials)
 * [Android Notes for Professionals](https://goalkicker.com/AndroidBook) - Compiled from StackOverflow Documentation (PDF)
 * [Android Programming Succinctly, Syncfusion](https://www.syncfusion.com/resources/techportal/ebooks/android) ([PDF](https://www.syncfusion.com/Account/Logon?ReturnUrl=%2fresources%2ftechportal%2febooks%2fandroid), [Kindle](https://www.syncfusion.com/Account/Logon?ReturnUrl=%2fresources%2ftechportal%2febooks%2fandroid)) (email address *requested*, not required)
 * [Android Tutorial](http://www.tutorialspoint.com/android) - Tutorials Point
 * [Codelabs for Advanced Android Development](https://developer.android.com/courses/advanced-training/toc)
 * [CodePath Android Cliffnotes](https://github.com/codepath/android_guides/wiki)
-* [Coreservlets Android Programming Tutorial](http://www.coreservlets.com/android-tutorial/)
 * [Expert Android and Eclipse development knowledge](http://www.vogella.com/tutorials/android.html)
 * [Google Android Developer Training](https://developer.android.com/guide)
 * [Styling Android](https://blog.stylingandroid.com)