Remove unnecessary includes of <signal.h>

These were once needed for sig_atomic_t, but that no longer appears in
these headers, so the include is not needed.

Reviewed-by: Shubham Khanna <Shubham.Khanna@fujitsu.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/cff5475d-e0a9-4561-b094-794aa36bd031%40eisentraut.org

src/include/replication/walsender.h

@@ -12,8 +12,6 @@
 #ifndef _WALSENDER_H
 #define _WALSENDER_H
 
-#include <signal.h>
-
 /*
  * What to do with a snapshot in create replication slot command.
  */

src/include/replication/worker_internal.h

@@ -12,8 +12,6 @@
 #ifndef WORKER_INTERNAL_H
 #define WORKER_INTERNAL_H
 
-#include <signal.h>
-
 #include "access/xlogdefs.h"
 #include "catalog/pg_subscription.h"
 #include "datatype/timestamp.h"