remove the obsolete hd driver

This driver is for pre-IDE hardisk that are only found in PC from the
stoneage of personal computing, and which we don't support elsewhere
in the kernel these days.

It's also been marked broken forever.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@fb.com>