MINOR: activity/fd: remove the dead_fd counter

This one is set whenever an FD is reported by a poller with a null owner,
regardless of the thread_mask. It has become totally meaningless because
it only indicates a migrated FD that was not yet reassigned to a thread,
but as soon as a thread uses it, the status will change to skip_fd. Thus
there is no reason to distinguish between the two, it adds more confusion
than it helps. Let's simply drop it.
diff --git a/include/haproxy/activity-t.h b/include/haproxy/activity-t.h
index 02fd2f3..63779ff 100644
--- a/include/haproxy/activity-t.h
+++ b/include/haproxy/activity-t.h
@@ -46,7 +46,6 @@
 	unsigned int poll_io;      // number of times poll() reported I/O events
 	unsigned int poll_exp;     // number of times poll() sees an expired timeout (includes wake_*)
 	unsigned int poll_drop_fd; // poller dropped a dead FD from the update list
-	unsigned int poll_dead_fd; // poller woke up with a dead FD
 	unsigned int poll_skip_fd; // poller skipped another thread's FD
 	unsigned int conn_dead;    // conn_fd_handler woke up on an FD indicating a dead connection
 	unsigned int stream_calls; // calls to process_stream()
diff --git a/include/haproxy/fd-t.h b/include/haproxy/fd-t.h
index 9923150..1e31825 100644
--- a/include/haproxy/fd-t.h
+++ b/include/haproxy/fd-t.h
@@ -113,7 +113,6 @@
 /* FD update status after fd_update_events() */
 enum {
 	FD_UPDT_DONE = 0,    // update done, nothing else to be done
-	FD_UPDT_DEAD,        // FD was already dead, ignore it
 	FD_UPDT_CLOSED,      // FD was closed
 	FD_UPDT_MIGRATED,    // FD was migrated, ignore it now
 };
diff --git a/src/cli.c b/src/cli.c
index d3411ed..3bc22cf 100644
--- a/src/cli.c
+++ b/src/cli.c
@@ -1414,7 +1414,6 @@
 	chunk_appendf(&trash, "poll_io:");      SHOW_TOT(thr, activity[thr].poll_io);
 	chunk_appendf(&trash, "poll_exp:");     SHOW_TOT(thr, activity[thr].poll_exp);
 	chunk_appendf(&trash, "poll_drop_fd:"); SHOW_TOT(thr, activity[thr].poll_drop_fd);
-	chunk_appendf(&trash, "poll_dead_fd:"); SHOW_TOT(thr, activity[thr].poll_dead_fd);
 	chunk_appendf(&trash, "poll_skip_fd:"); SHOW_TOT(thr, activity[thr].poll_skip_fd);
 	chunk_appendf(&trash, "conn_dead:");    SHOW_TOT(thr, activity[thr].conn_dead);
 	chunk_appendf(&trash, "stream_calls:"); SHOW_TOT(thr, activity[thr].stream_calls);
diff --git a/src/fd.c b/src/fd.c
index df9b5de..3ac7e55 100644
--- a/src/fd.c
+++ b/src/fd.c
@@ -459,12 +459,6 @@
 
 	ti->flags &= ~TI_FL_STUCK; // this thread is still running
 
-	/* do nothing on remains of an old dead FD */
-	if (!fdtab[fd].owner) {
-		activity[tid].poll_dead_fd++;
-		return FD_UPDT_DEAD;
-	}
-
 	/* do nothing if the FD was taken over under us */
 	if (fd_set_running(fd) == -1) {
 		activity[tid].poll_skip_fd++;