books: drop "content under development" banners

Author: Steve Hollasch

books/RayTracingInOneWeekend.html

@@ -13,12 +13,6 @@
 Overview
 ====================================================================================================
 
-
-!!! ERROR: Content Under Development
-    See [the official release page](https://github.com/RayTracing/raytracing.github.io/releases/)
-    for latest official PDF version.
-
-
 I’ve taught many graphics classes over the years. Often I do them in ray tracing, because you are
 forced to write all the code but you can still get cool images with no API. I decided to adapt my
 course notes into a how-to, to get you to a cool program as quickly as possible. It will not be a

books/RayTracingTheNextWeek.html

@@ -15,11 +15,6 @@
 Overview
 ====================================================================================================
 
-!!! ERROR: Content Under Development
-    See [the official release page](https://github.com/RayTracing/raytracing.github.io/releases/)
-    for latest official PDF version.
-
-
 In Ray Tracing in One Weekend, you built a simple brute force path tracer. In this installment we’ll
 add textures, volumes (like fog), rectangles, instances, lights, and support for lots of objects
 using a BVH. When done, you’ll have a “real” ray tracer.

books/RayTracingTheRestOfYourLife.html

@@ -15,13 +15,7 @@
 Overview
 ====================================================================================================
 
-
-!!! ERROR: Content Under Development
-    See [the official release page](https://github.com/RayTracing/raytracing.github.io/releases/)
-    for latest official PDF version.
-
-
-In _Ray Tracing In One Weekend_ and _Ray Tracing: the Next Week_, you built a “real” ray tracer.
+In _Ray Tracing in One Weekend_ and _Ray Tracing: the Next Week_, you built a “real” ray tracer.
 
 In this volume, I assume you will be pursuing a career related to ray tracing and we will dive into
 the math of creating a very serious ray tracer. When you are done you should be ready to start