Re-enable accumulating transfer failure log files for command-line actions

This was disabled in commit 7ca8bf3321d1b62ea4e817e28914ed2fa56afe30,
because only the assistant used them, and they were clutter. But, now
--failed also uses them.

Remove the failure log files after successful transfers. Should avoid
most of the clutter problems.

Commit 7ca8bf3321d1b62ea4e817e28914ed2fa56afe30 mentions a subtle behavior
change, which has now been reverted:

    There is one behavior change from this. If glacier is being used, and a
    manual git annex get --from glacier fails because the file isn't available
    yet, the assistant will no longer later see that failed transfer file and
    retry the get.

0 files changed, 0 insertions, 0 deletions