Windows: registry enum do not request write perm

Only Read and Query privileges are required to enumerate the registry
keys, do not request write privileges for an enumeration.

Change-Id: Ifc9acb4203db71b6e94bf5a21ca5aa104d94d35b
Reviewed-on: http://gerrit.openafs.org/11416
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>