klog.krb5 -lifetime is not implemented

klog.krb5 -lifetime is not implemented

The klog.krb5 -lifetime option was copied from earlier versions of log
and klog, which had the ability to set the krb4 token lifetime. However,
the -lifetime option is not feasible the krb5 version, and so is not
implemented in klog.krb5.

Update the klog.krb5 man page to document the -lifetime option has no
effect.  Remove the code which unnecessarily checks the unused klog.krb5
-lifetime command line argument.

The unused lifetime variable was discovered by Pat Riehecky using the
clang scan-build static analyzer.

Change-Id: I5f459ec46eaff87a69ccdf7de386a671d0944a5a
Reviewed-on: https://gerrit.openafs.org/13309
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: PatRiehecky <jcpunk@gmail.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>