Move the prototype for the internal OS from from sched/sched/sched.h to include/nuttx/sched.h. This was done because binfmt/binfmt/excecmodule.c requires the prototype for sched_releasetcb() and was illegally including sched/sched/sched.h. That is a blatant violation of the OS modular design and the person that did this should be hung up by their thumbs. Oh... I did that back in a bad moment in 2014. Now that is made right.