docbook: fix broken media build

DocBook/v4l/ no longer has any *.png files, so the 'cp' command fails,
breaking the build.  Drop the *.png cp.

  cp: cannot stat `linux-2.6.38-git18/Documentation/DocBook/v4l/*.png': No such file or directory
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/DocBook/Makefile

@@ -55,7 +55,6 @@ mandocs: $(MAN)
 build_images = mkdir -p $(objtree)/Documentation/DocBook/media/ && \
 	       cp $(srctree)/Documentation/DocBook/dvb/*.png \
 	          $(srctree)/Documentation/DocBook/v4l/*.gif \
-	          $(srctree)/Documentation/DocBook/v4l/*.png \
 		  $(objtree)/Documentation/DocBook/media/
 
 xmldoclinks: