Remove trailing whitespace in default /etc/selinux/config
    
    See <https://pagure.io/atomic-wg/issue/341> - basically for libostree
    (and hence rpm-ostree, and Fedora Editions that use it like Fedora Atomic Host),
    the Anaconda `selinux --enforcing` verb will end up rewriting
    `/etc/selinux/config` to the same value it had before.
    
    But because of the trailing space character, this generates
    a difference, and means the config file appears locally modified,
    and hence deployed systems won't receive updates.
    
    I think Anaconda should also be fixed to avoid touching the file *at all*
    if it wouldn't result in a change, but let's remove the trailing space
    here too, as it's better to fix in two places.