afsd: deprecate afsd -settime

afsd: deprecate afsd -settime

Print a warning message if -settime is given and update the afsd man
page to declare that -settime is deprecated.

Thanks to Stephan Wiesand for suggesting this change.  This is a 1.6.x
specific change.

Change-Id: Iab3f9aa602552e88d74b04e4628c7af13e0439e3
Reviewed-on: https://gerrit.openafs.org/12207
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>