xdriver_xf86-video-sunffb: remove package

The FFB was an old SBUS video card used in Sun SPARC workstations
from the 90s.
Highly unlikely a target for buildroot.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>