vmwgfx: Remove the fifo debug ioctl

It was only used for bringup debugging, and probably doesn't work
anymore. Remove it.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>