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/defs.h b/defs.h
index d340cbd..ab24f7c 100644
--- a/defs.h
+++ b/defs.h
@@ -368,9 +368,8 @@
 	struct timeval etime;	/* Syscall entry time */
 				/* Support for tracing forked processes */
 	struct tcb *parent;	/* Parent of this process */
-	int nchildren;		/* # of traced children */
 #ifdef LINUX
-	int nclone_threads;	/* # of nchildren with CLONE_THREAD */
+	int nclone_threads;	/* # of children with CLONE_THREAD */
 #endif
 				/* (1st arg of wait4()) */
 	long baddr;		/* `Breakpoint' address */