sched: replace sync pause with async pause for nxtask_terminate

reason:
In the kernel, we are planning to remove all occurrences of up_cpu_pause as one of the steps to
simplify the implementation of critical sections. The goal is to enable spin_lock_irqsave to encapsulate critical sections,
thereby facilitating the replacement of critical sections(big lock) with smaller spin_lock_irqsave(small lock)

Signed-off-by: hujun5 <hujun5@xiaomi.com>

arch/x86/src/common/x86_exit.c

@@ -55,12 +55,6 @@ void up_exit(int status)
 {
   struct tcb_s *tcb = this_task();
 
-  /* Make sure that we are in a critical section with local interrupts.
-   * The IRQ state will be restored when the next task is started.
-   */
-
-  enter_critical_section();
-
   /* Destroy the task at the head of the ready to run list. */
 
   nxtask_exit();