Remove completed tasks from todo list, add info about git/gerrit preference

Removed completed tasks (fstrace subcommand help in-binary and issue with
-noexecute vs. -dryrun in vos delentry) from todo list.  Added info about
git/gerrit preference for documentation help, but patches still allowed
to the openafs-doc list.

Reviewed-on: http://gerrit.openafs.org/4803
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 8f186c0f7a48059ca561422d58073e22934ea2dc)

Change-Id: Iec6e3db185e816f6c1b587cc74cc5ca5a2c93282
Reviewed-on: http://gerrit.openafs.org/9503
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>