Remove the private undocumented function
_PyEval_GetCoroutineOriginTrackingDepth() from the C API. Call the
public sys.get_coroutine_origin_tracking_depth() function instead.

Change the internal function
_PyEval_SetCoroutineOriginTrackingDepth():

* Remove the 'tstate' parameter;
* Add return value and raises an exception if depth is negative;
* No longer export the function: call the public
  sys.set_coroutine_origin_tracking_depth() function instead.

Uniformize also function declarations in pycore_ceval.h.