agp: kill agp_flush_chipset and corresponding ioctl

The intel drm calls the chipset functions now directly. Userspace
never called the corresponding ioctl, hence it can be killed, too.

Cc: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/char/agp/compat_ioctl.c

@@ -276,7 +276,6 @@ long compat_agp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		break;
 
 	case AGPIOC_CHIPSET_FLUSH32:
-		ret_val = agpioc_chipset_flush_wrap(curr_priv);
 		break;
 	}