vos: Remove unused 'done' loop variable

In SendFile we break at the same time as setting the done flag,
so its value is never checked. Just remove it as it is redundant
with the current loop logic.

Caught by clang-analyzer

Change-Id: Ibf8f756b06fd26cb2013ece97eb9196c71ad88bd
Reviewed-on: http://gerrit.openafs.org/9164
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>