fix schedrelease() syscall

kernel/syscall/sched.c

@@ -7,11 +7,5 @@
 #include "hal/hal.h"
 
 int32_t SYSCALL0(sys_schedrelease) {
-  spinlock_acquire(&PROCS.spinlock);
-  Proc *proc = PROCS.current;
-  spinlock_release(&PROCS.spinlock);
-
-  /* proc_sched((void *)frame); */
-
-  return E_OK;
+  return E_DOSCHEDULING;
 }