REORG: include: move signal.h to haproxy/signal{,-t}.h

No change was necessary. Include from wdt.c was dropped since unneeded.
diff --git a/src/peers.c b/src/peers.c
index e1a2525..c1c9588 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -26,6 +26,7 @@
 #include <haproxy/net_helper.h>
 #include <haproxy/obj_type-t.h>
 #include <haproxy/task.h>
+#include <haproxy/signal.h>
 #include <haproxy/time.h>
 #include <haproxy/tools.h>
 #include <haproxy/thread.h>
@@ -43,7 +44,6 @@
 #include <proto/proxy.h>
 #include <proto/session.h>
 #include <proto/stream.h>
-#include <proto/signal.h>
 #include <proto/stick_table.h>
 #include <proto/stream_interface.h>