nonplat_property_contexts: use fc_sort vs sort

sort respects locale settings, so the value of LC_ALL can affect
how sort orders things. This can cause labeling issues.

More information on locale and sort can be found via:
  * locale(1) - man 1 locale
  * sort(1) - man 1 sort
  * https://debbugs.gnu.org/cgi/bugreport.cgi?bug=28539



Rather than deal with this locale setting use fc_sort on
property contexts. This also has the side-effect of
stripping comments, and thus sed can be dropped.

Test: This was tested by:
  * comparing outputs to previous runs
  * compile tested *only*.

Change-Id: I1e1eb4dff76f717b5f82f697e677a108abb69892
Signed-off-by: William Roberts <william.c.roberts@intel.com>