selinux.c: do not use deprecated typedef and skip context translation

selinux.c: do not use deprecated typedef and skip context translation

These retrieved contexts are just passed to libselinux functions and not
printed or otherwise made available to the outside, so a context
translation to human readable MCS/MLS labels is not needed.
(see man:setrans.conf(5))

The typedef security_context_t is deprecated, see
https://github.com/SELinuxProject/selinux/commit/9eb9c9327563014ad6a807814e7975424642d5b9

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Acked-by: James Carter <jwcart2@gmail.com>