Fixes lost RC on px4fmu-v4

   A recent change in in the fmu stops the instance when a
   xxxx_reset command is used issued if the fmu was not
   already running.

   That change left publications published and then on the
   next creation created a new publications was created.

   This change calls orb_unadvertise to mark the publication
   as un published so that on the next instantiations of the
   fmu it resumes publishing on the same publication.