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/namespace.c b/src/namespace.c
index 616dbea..dfda7a5 100644
--- a/src/namespace.c
+++ b/src/namespace.c
@@ -14,8 +14,8 @@
 #include <haproxy/namespace.h>
 #include <haproxy/hash.h>
 #include <haproxy/errors.h>
+#include <haproxy/signal.h>
 #include <proto/log.h>
-#include <proto/signal.h>
 
 /* Opens the namespace <ns_name> and returns the FD or -1 in case of error
  * (check errno).