block: rename bio_iov_iter_get_pages_aligned to bio_iov_iter_get_pages

Now that the bio_iov_iter_get_pages is free again, use it instead of
the more complicated now.  Also drop the unused export.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>