Remove obsolete check in SIGTERM handler for the startup process.

Thanks to commit 3b00fdba9f, this check in the SIGTERM handler for
the startup process is now obsolete and can be removed.  Instead of
leaving around the dead function write_stderr_signal_safe(), I've
opted to just remove it for now.

This partially reverts commit 97550c0711.

Reviewed-by: Andres Freund, Noah Misch
Discussion: https://postgr.es/m/20231121212008.GA3742740%40nathanxps13

src/backend/postmaster/startup.c

@@ -19,8 +19,6 @@
  */
 #include "postgres.h"
 
-#include <unistd.h>
-
 #include "access/xlog.h"
 #include "access/xlogrecovery.h"
 #include "access/xlogutils.h"
@@ -112,20 +110,7 @@ static void
 StartupProcShutdownHandler(SIGNAL_ARGS)
 {
 	if (in_restore_command)
-	{
+		proc_exit(1);
-		/*
-		 * If we are in a child process (e.g., forked by system() in
-		 * RestoreArchivedFile()), we don't want to call any exit callbacks.
-		 * The parent will take care of that.
-		 */
-		if (MyProcPid == (int) getpid())
-			proc_exit(1);
-		else
-		{
-			write_stderr_signal_safe("StartupProcShutdownHandler() called in child process\n");
-			_exit(1);
-		}
-	}
 	else
 		shutdown_requested = true;
 	WakeupRecovery();

src/backend/utils/error/elog.c

@@ -3737,31 +3737,3 @@ write_stderr(const char *fmt,...)
 #endif
 	va_end(ap);
 }
-
-
-/*
- * Write a message to STDERR using only async-signal-safe functions.  This can
- * be used to safely emit a message from a signal handler.
- *
- * TODO: It is likely possible to safely do a limited amount of string
- * interpolation (e.g., %s and %d), but that is not presently supported.
- */
-void
-write_stderr_signal_safe(const char *str)
-{
-	int			nwritten = 0;
-	int			ntotal = strlen(str);
-
-	while (nwritten < ntotal)
-	{
-		int			rc;
-
-		rc = write(STDERR_FILENO, str + nwritten, ntotal - nwritten);
-
-		/* Just give up on error.  There isn't much else we can do. */
-		if (rc == -1)
-			return;
-
-		nwritten += rc;
-	}
-}

src/include/utils/elog.h

@@ -536,10 +536,4 @@ extern void write_jsonlog(ErrorData *edata);
  */
 extern void write_stderr(const char *fmt,...) pg_attribute_printf(1, 2);
 
-/*
- * Write a message to STDERR using only async-signal-safe functions.  This can
- * be used to safely emit a message from a signal handler.
- */
-extern void write_stderr_signal_safe(const char *fmt);
-
 #endif							/* ELOG_H */