Restore original prototype of mp_sched_schedule

[amirgon]

This is important for compatability with libraries that call mp_sched_schedule and need to compile on both the original Microptython and lobo's Micropython. New prototype name changed to mp_sched_schedule_ex

[loboris]

There are reasons why the mp_sched_schedule was changed.
If writing the C-module wich uses mp_sched_schedule for both original MicroPython and this port, it should be easy to conditionally compile for one or the other, something like this

#if MICROPY_PY_SYS_PLATFORM_LOBO
#define mymp_sched_schedule(x) mp_sched_schedule(x, NULL);
#else
#define mymp_sched_schedule(x) mp_sched_schedule(x);
#endif

then use mymp_sched_schedule() instead of mp_sched_schedule in your module.
It is simple and should work.

[amirgon]

@loboris
I understand there are reasons for the change, that is why I kept your version as mp_sched_schedule_ex.
However, in my opinion it's cleaner to keep the same API, instead of adding #ifs and changing all calls to mp_sched_schedule.

With my PR, when you have a Micropython library that uses mp_sched_schedule it would work without a change on your branch. With your suggestion, such library would have to be adapted by changing each mp_sched_schedule call to mymp_sched_schedule.