xdriver_xf86-video-suncg6: remove package

The CG6 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>