documentation/poky-ref-manual: Figures cleanup

I removed two figures from the figures directory:
cropped-yocto-project-bw.png and yocto-project-transp.png.
Both figures are relics and not used in the manual.  I also
altered the Makefile to pull the ss-sato.png file from the
figures directory instead of the screenshots directory.  I moved
this PNG file from the screenshots directory to the figures
directory so that all figures would be in the figures directory.
Finally, I updated the introduction.xml file so that the html
code to include the ss-sato.png file pulls it from the figures
directory and not the screenshots directory.

(From yocto-docs rev: 4b900cf71a3a87d86bd14ce2056310484daf8081)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/poky-ref-manual/introduction.xml

@@ -59,7 +59,7 @@
     <screenshot>
     <mediaobject>
         <imageobject>
-            <imagedata fileref="screenshots/ss-sato.png" format="PNG" align='center' scalefit='1' width="100%" contentdepth="100%"/>
+            <imagedata fileref="figures/ss-sato.png" format="PNG" align='center' scalefit='1' width="100%" contentdepth="100%"/>
         </imageobject>
         <caption>
             <para>The Sato Desktop - A screenshot from a machine running a Poky built image</para>