documentation: Moved devtool workflow to sdk manual

Fixes [YOCTO #11630]

The section on the devtool workflow in the dev-manual was 99%
identical to what was in the sdk-manual.  I have moved the
workflow procedure from the old "Model" chapter of the dev-manual
to be merged with what was in the sdk-manual.  In truth, the
only things added were a note about devtool not being exclusive
to SDK development.

The result of moving (deleting) this section was that the "model"
chapter of the dev-manual went away.  The devtool stuff, Quilt,
devshell, and python shell are all out now and there is no
chapter left.  So, mega-manual had to be adjusted to not pull that
chapter in when building the dev-manual.  I had to delete three
figures that were used in the flow.  The figures were already
replicated in the sdk-manual.  The figures were deleted from the
figures folder of both the dev-manual and the mega-manual.

I had to make sure all references to the old devtool stuf in the
YP doc set were adjusted.

(From yocto-docs rev: 5dbd643d31ab502df53a22229e457a03da7772b7)

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

documentation/mega-manual/mega-manual.xml

@@ -130,8 +130,6 @@
         xmlns:xi="http://www.w3.org/2003/XInclude" href="../dev-manual/dev-manual-start.xml"/>
     <xi:include
         xmlns:xi="http://www.w3.org/2003/XInclude" href="../dev-manual/dev-manual-newbie.xml"/>
-    <xi:include
-        xmlns:xi="http://www.w3.org/2003/XInclude" href="../dev-manual/dev-manual-model.xml"/>
     <xi:include
         xmlns:xi="http://www.w3.org/2003/XInclude" href="../dev-manual/dev-manual-common-tasks.xml"/>
     <xi:include