mega-manual.xml: Removed the getting-started-concepts.xml file

mega-manual.xml: Removed the getting-started-concepts.xml file

Because the deeper concepts chapter that was in the Getting Started
With Yocto Project Manual was moved to a new Yocto Project Concepts
Manual, I had to delete it from the mega-manual.xml file where it
would be included as a chapter in the getting-started manual.

(From yocto-docs rev: a6847cc90cd0e35e275dd4cf080067ecbe5d4361)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>