block: remove biodoc.rst

This document is completely out of date and extremely misleading. In
general the existing kerneldoc comment serve as a much better
documentation of the still existing functionality, while the history
blurbs are pretty much irrelevant today.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20220215081047.3693582-1-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>