kernel-dev: Eliminated "Generating Configuration Files" section.

kernel-dev: Eliminated "Generating Configuration Files" section.

This section was largely redundant now.  The small things that did
add value I placed in other areas of the chapter 2.  One was a new
section on expanding variables using bitbake -e.  Another was a bit
about the defconfig file.  And a small procedure on how to create
config fragments using the "diffconfig" command was retained.

Links from the dev-manual and the ref-manual were adjusted as well.

(From yocto-docs rev: 7059d3eac1fec20089cabf197503f1bec747686d)

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