arch: _exit should't call nxsched_resume_scheduler twice in SMP mode

utilize the call inside nxtask_exit instead, also move
nxsched_suspend_scheduler to nxtask_exit for symmetry

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Change-Id: I219fc15faf0026e452b0db3906aa40b40ac677f3

arch/z80/src/common/z80_exit.c

@@ -142,10 +142,6 @@ void _exit(int status)
   nxsched_foreach(_up_dumponexit, NULL);
 #endif
 
-  /* Update scheduler parameters */
-
-  nxsched_suspend_scheduler(tcb);
-
   /* Destroy the task at the head of the ready to run list. */
 
   nxtask_exit();
@@ -167,10 +163,6 @@ void _exit(int status)
   group_addrenv(tcb);
 #endif
 
-  /* Reset scheduler parameters */
-
-  nxsched_resume_scheduler(tcb);
-
   /* Then switch contexts */
 
   RESTORE_USERCONTEXT(tcb);