block: remove REQ_NOWAIT_INLINE

We had a few issues with this code, and there's still a problem around
how we deal with error handling for chained/split bios. For now, just
revert the code and we'll try again with a thoroug solution. This
reverts commits:

e15c2ffa ("block: fix O_DIRECT error handling for bio fragments")
0eb6ddfb ("block: Fix __blkdev_direct_IO() for bio fragments")
6a43074e ("block: properly handle IOCB_NOWAIT for async O_DIRECT IO")
893a1c97

 ("blk-mq: allow REQ_NOWAIT to return an error inline")

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