staging: remove the b3dfg driver

It has no users, and no developers to maintain it to get
it merged into mainline.

So sad.

Cc: Daniel Drake <ddrake@brontes3d.com>
Cc: Justin Bronder <jsbronder@brontes3d.com>
Cc: Duane Griffin <duaneg@dghda.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>