groff: not ship /usr/bin/grap2graph

grap2graph which converts a GRAP diagram into a cropped image fails
to run as below:
 $ grap2graph
 /usr/bin/grap2graph: line 89: convert: command not found
 /usr/bin/grap2graph: warning: falling back to old '-crop 0x0' trim method
 /usr/bin/grap2graph: line 104: convert: command not found
 /usr/bin/grap2graph: line 103: grap: command not found

Considering we don't often need to convert a GRAP diagram into
a cropped image and the recipe ImageMagick which provides convert
command is in meta-oe layer, so don't ship the related files to
avoid the confusion about the above run time error.

Signed-off-by: Mingli Yu <mingli.yu@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>