rx: Remove obsolete comment

This comment refers to the fact that we used to be just checking for
SELinux to see if we should pass that extra argument. Ever since
commit cb1b41b159b98881f66319d7f65d941ba9fab911, we do have a better
test for this.

Reviewed-on: http://gerrit.openafs.org/10593
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
(cherry picked from commit 2ed7023b26acb3277e42eac803a0702b95167e6e)

Change-Id: I5a8ebcda7fcb85931638ab0bec807b1da8ebed3f
Reviewed-on: http://gerrit.openafs.org/10597
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>