Remove unused latch

It was left unused by commit bc971f4, which replaced the latch
usage with a condition variable

Discussion: https://www.postgresql.org/message-id/391abe21-413e-4d91-a650-b663af49500c@iki.fi

Author: hlinnaka

src/backend/replication/walsender.c

@@ -2935,7 +2935,6 @@ InitWalSenderSlot(void)
 			walsnd->flushLag = -1;
 			walsnd->applyLag = -1;
 			walsnd->sync_standby_priority = 0;
-			walsnd->latch = &MyProc->procLatch;
 			walsnd->replyTime = 0;
 
 			/*
@@ -2979,8 +2978,6 @@ WalSndKill(int code, Datum arg)
 	MyWalSnd = NULL;
 
 	SpinLockAcquire(&walsnd->mutex);
-	/* clear latch while holding the spinlock, so it can safely be read */
-	walsnd->latch = NULL;
 	/* Mark WalSnd struct as no longer being in use. */
 	walsnd->pid = 0;
 	SpinLockRelease(&walsnd->mutex);

src/include/replication/walsender_private.h

@@ -18,7 +18,6 @@
 #include "nodes/replnodes.h"
 #include "replication/syncrep.h"
 #include "storage/condition_variable.h"
-#include "storage/latch.h"
 #include "storage/shmem.h"
 #include "storage/spin.h"
 
@@ -71,12 +70,6 @@ typedef struct WalSnd
 	/* Protects shared variables in this structure. */
 	slock_t		mutex;
 
-	/*
-	 * Pointer to the walsender's latch. Used by backends to wake up this
-	 * walsender when it has work to do. NULL if the walsender isn't active.
-	 */
-	Latch	   *latch;
-
 	/*
 	 * Timestamp of the last message received from standby.
 	 */