block: unexport DISK_EVENT_MEDIA_CHANGE for legacy/fringe drivers

In-kernel disk event polling doesn't matter for legacy/fringe drivers
and may lead to infinite event loop if ->check_events() implementation
generates events on level condition instead of edge.

Now that block layer supports suppressing exporting unlisted events,
simply leaving disk->events cleared allows these drivers to keep the
internal revalidation behavior intact while avoiding weird
interactions with userland event handler.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

drivers/message/i2o/i2o_block.c

@@ -1000,7 +1000,6 @@ static struct i2o_block_device *i2o_block_device_alloc(void)
 	gd->major = I2O_MAJOR;
 	gd->queue = queue;
 	gd->fops = &i2o_block_fops;
-	gd->events = DISK_EVENT_MEDIA_CHANGE;
 	gd->private_data = dev;
 
 	dev->gd = gd;