Remove write-only nchildren member from struct tcb

* defs.h: Remove nchildren member from struct tcb.
* process.c (handle_new_child): Remove inc/decrements of tcp->nchildren.
  (internal_fork): Likewise.
* strace.c (startup_attach): Likewise.
  (droptcb): Likewise.
  (alloc_tcb): Remove initialization of tcp->nchildren.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
diff --git a/strace.c b/strace.c
index 6fb6fd6..94559a5 100644
--- a/strace.c
+++ b/strace.c
@@ -514,7 +514,6 @@
 					else if (tid != tcbtab[tcbi]->pid) {
 						tcp = alloctcb(tid);
 						tcp->flags |= TCB_ATTACHED|TCB_CLONE_THREAD|TCB_FOLLOWFORK;
-						tcbtab[tcbi]->nchildren++;
 						tcbtab[tcbi]->nclone_threads++;
 						tcp->parent = tcbtab[tcbi];
 					}
@@ -1284,7 +1283,6 @@
 		if ((tcp->flags & TCB_INUSE) == 0) {
 			tcp->pid = pid;
 			tcp->parent = NULL;
-			tcp->nchildren = 0;
 #ifdef TCB_CLONE_THREAD
 			tcp->nclone_threads = 0;
 #endif
@@ -1662,15 +1660,14 @@
 	tcp->pid = 0;
 
 	if (tcp->parent != NULL) {
-		tcp->parent->nchildren--;
 #ifdef TCB_CLONE_THREAD
 		if (tcp->flags & TCB_CLONE_THREAD)
 			tcp->parent->nclone_threads--;
 #endif
 #ifdef LINUX
-		/* Update `tcp->parent->parent->nchildren' and the other fields
-		   like NCLONE_DETACHED, only for zombie group leader that has
-		   already reported and been short-circuited at the top of this
+		/* Update fields like NCLONE_DETACHED, only
+		   for zombie group leader that has already reported
+		   and been short-circuited at the top of this
 		   function.  The same condition as at the top of DETACH.  */
 		if ((tcp->flags & TCB_CLONE_THREAD) &&
 		    tcp->parent->nclone_threads == 0 &&