Revert "sched/group/setuptask_file: duplicate idle task fd for kernel thread"

let's using shared group for kthreads, see pull/12320

This reverts commit 4e24eec.

Author: Donny9

sched/group/group_setuptaskfiles.c

@@ -66,7 +66,7 @@ int group_setuptaskfiles(FAR struct task_tcb_s *tcb,
   FAR struct task_group_s *group = tcb->cmn.group;
   int ret = OK;
 #ifndef CONFIG_FDCLONE_DISABLE
-  FAR struct tcb_s *rtcb;
+  FAR struct tcb_s *rtcb = this_task();
 #endif
 
   sched_trace_begin();
@@ -77,20 +77,7 @@ int group_setuptaskfiles(FAR struct task_tcb_s *tcb,
 #endif
 
 #ifndef CONFIG_FDCLONE_DISABLE
-
-  /* The The file descriptors of kernel threads should be clean and
-   * should not be generated based on user threads. Instead, an idle
-   * thread should be chosen.
-   */
-
-  if ((tcb->cmn.flags & TCB_FLAG_TTYPE_MASK) == TCB_FLAG_TTYPE_KERNEL)
-    {
-      rtcb = &g_idletcb[this_cpu()];
-    }
-  else
-    {
-      rtcb = this_task();
-    }
+  DEBUGASSERT(rtcb->group);
 
   /* Duplicate the parent task's file descriptors */
 

sched/init/nx_start.c

@@ -209,7 +209,7 @@ volatile uint8_t g_nx_initstate;  /* See enum nx_initstate_e */
  * bringing up the rest of the system.
  */
 
-struct tcb_s g_idletcb[CONFIG_SMP_NCPUS];
+static struct tcb_s g_idletcb[CONFIG_SMP_NCPUS];
 
 /* This is the name of the idle task */
 

sched/sched/sched.h

@@ -204,16 +204,6 @@ extern FAR struct tcb_s *g_delivertasks[CONFIG_SMP_NCPUS];
 
 extern FAR struct tcb_s *g_running_tasks[CONFIG_SMP_NCPUS];
 
-/* This is an array of task control block (TCB) for the IDLE thread of each
- * CPU.  For the non-SMP case, this is a a single TCB; For the SMP case,
- * there is one TCB per CPU.  NOTE: The system boots on CPU0 into the IDLE
- * task.  The IDLE task later starts the other CPUs and spawns the user
- * initialization task.  That user initialization task is responsible for
- * bringing up the rest of the system.
- */
-
-extern struct tcb_s g_idletcb[CONFIG_SMP_NCPUS];
-
 /* This is the list of all tasks that are ready-to-run, but cannot be placed
  * in the g_readytorun list because:  (1) They are higher priority than the
  * currently active task at the head of the g_readytorun list, and (2) the