Remove references to PG_VERSION_NUM in bgworker modules

Those modules will not be able to work with older versions than
Postgres 10 if left as-is, so let's keep life simple.

count_relations/count_relations.c

@@ -147,12 +147,6 @@ _PG_init(void)
 	snprintf(worker.bgw_name, BGW_MAXLEN, "count relations");
 	worker.bgw_restart_time = BGW_NEVER_RESTART;
 	worker.bgw_main_arg = (Datum) 0;
-#if PG_VERSION_NUM >= 90400
-	/*
-	 * Notify PID is present since 9.4. If this is not initialized
-	 * a static background worker cannot start properly.
-	 */
 	worker.bgw_notify_pid = 0;
-#endif
 	RegisterBackgroundWorker(&worker);
 }

hello_notify/hello_notify.c

@@ -265,12 +265,6 @@ _PG_init(void)
 	worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
 	worker.bgw_restart_time = 10;
 	worker.bgw_main_arg = (Datum) 0;
-#if PG_VERSION_NUM >= 90400
-	/*
-	 * Notify PID is present since 9.4. If this is not initialized
-	 * a static background worker cannot start properly.
-	 */
 	worker.bgw_notify_pid = 0;
-#endif
 	RegisterBackgroundWorker(&worker);
 }

hello_signal/hello_signal.c

@@ -123,12 +123,6 @@ _PG_init(void)
 	/* Wait 10 seconds for restart before crash */
 	worker.bgw_restart_time = 10;
 	worker.bgw_main_arg = (Datum) 0;
-#if PG_VERSION_NUM >= 90400
-	/*
-	 * Notify PID is present since 9.4. If this is not initialized
-	 * a static background worker cannot start properly.
-	 */
 	worker.bgw_notify_pid = 0;
-#endif
 	RegisterBackgroundWorker(&worker);
 }

hello_world/hello_world.c

@@ -98,12 +98,6 @@ _PG_init(void)
 	snprintf(worker.bgw_name, BGW_MAXLEN, "hello world");
 	worker.bgw_restart_time = BGW_NEVER_RESTART;
 	worker.bgw_main_arg = (Datum) 0;
-#if PG_VERSION_NUM >= 90400
-	/*
-	 * Notify PID is present since 9.4. If this is not initialized
-	 * a static background worker cannot start properly.
-	 */
 	worker.bgw_notify_pid = 0;
-#endif
 	RegisterBackgroundWorker(&worker);
 }

kill_idle/kill_idle.c

@@ -236,12 +236,6 @@ _PG_init(void)
 	/* Wait 10 seconds for restart before crash */
 	worker.bgw_restart_time = 10;
 	worker.bgw_main_arg = (Datum) 0;
-#if PG_VERSION_NUM >= 90400
-	/*
-	 * Notify PID is present since 9.4. If this is not initialized
-	 * a static background worker cannot start properly.
-	 */
 	worker.bgw_notify_pid = 0;
-#endif
 	RegisterBackgroundWorker(&worker);
 }