Windows: Strip out unused ModWriter Fastio code

Windows: Strip out unused ModWriter Fastio code

The code is no longer used (the fcb->PagingIO resource is taken for
us by the modwriter) so we strip it out to save other making changes
and then remembering/discovering that this code isn't being used.

Change-Id: I0d880049758559ae0860f8c1e12583304a459a68
Reviewed-on: http://gerrit.openafs.org/10191
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>