Windows: memory leak when setting tokens via smb

Windows: memory leak when setting tokens via smb

The SID string of the RPC used to set the token sessionKey
was being leaked.  Be sure to free it when it is no longer
required.

Reviewed-on: http://gerrit.openafs.org/6244
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
(cherry picked from commit f30d70ba5575753302be0a2b08c27a639898d4aa)

Change-Id: I1133b50841919ca5957081c82625c2b1607c34ae
Reviewed-on: http://gerrit.openafs.org/6815
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>