Remove function declaration for function in pg_proc.

The declaration is automatically generated. Noticed when experimenting with
adding PGDLLIMPORT markers for functions.

Discussion: https://postgr.es/m/20220512164513.vaheofqp2q24l65r@alap3.anarazel.de

Author: anarazel

src/backend/replication/logical/launcher.c

@@ -42,6 +42,7 @@
 #include "storage/procarray.h"
 #include "storage/procsignal.h"
 #include "tcop/tcopprot.h"
+#include "utils/builtins.h"
 #include "utils/memutils.h"
 #include "utils/pg_lsn.h"
 #include "utils/ps_status.h"
@@ -75,8 +76,6 @@ static void logicalrep_worker_cleanup(LogicalRepWorker *worker);
 
 static bool on_commit_launcher_wakeup = false;
 
-Datum		pg_stat_get_subscription(PG_FUNCTION_ARGS);
-
 
 /*
  * Load the list of subscriptions.