Windows: remove last bits of BIOD from Direct Store

Direct I/O Store operations are performed directly against a memory
buffer stored in the background direct store rock structure.  There is no
BIOD used in the current implementation.  Remove the BIOD from the call
stack.

Change-Id: I78d7b898a6eec5eb39c943e760a678913b42bf0d
Reviewed-on: http://gerrit.openafs.org/9607
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>