Remove redundant fetch of the recent flush pointer in WalSndWaitForWal.

In WalSndWaitForWal(), we fetch a recent flush pointer both outside the
loop and inside the loop. But we start using RecentFlushPtr only after we
fetch it inside the loop. So we can remove one outside the loop.

Author: Shveta Malik
Reviewed-by: Bertrand Drouvot, Matthias van de Meent, Amit Kapila
Discussion: https://postgr.es/m/CAJpy0uBSCQz1yMD-WiEthzEe23dti2-Kr_pitVb7vAPFbFKm=A@mail.gmail.com

src/backend/replication/walsender.c

@@ -1831,12 +1831,6 @@ WalSndWaitForWal(XLogRecPtr loc)
 		!NeedToWaitForWal(loc, RecentFlushPtr, &wait_event))
 		return RecentFlushPtr;
 
-	/* Get a more recent flush pointer. */
-	if (!RecoveryInProgress())
-		RecentFlushPtr = GetFlushRecPtr(NULL);
-	else
-		RecentFlushPtr = GetXLogReplayRecPtr(NULL);
-
 	/*
 	 * Within the loop, we wait for the necessary WALs to be flushed to disk
 	 * first, followed by waiting for standbys to catch up if there are enough