scheduler: Disable load tracking when not needed
kernel: Remove cpu_info::load

This field forces kernel to track each CPU load all the time. It is not
a problem with the current scheduler on a multicore systems, but on
single core machnies or with any other future scheduler this field may
become just an unnecessary burden. It isn't difficult for an application
to compute CPU load by itself when it needs it.
scheduler: SCHEDULER_EXIT_FUNCTION() is not needed