Better fix for "unarchived WAL files get deleted on crash recovery" bug.

Revert my earlier fix for the bug that unarchived WAL files get deleted on
crash recovery, commit c9cc7e05c6. We create
a .done file for files streamed or restored from archive, so the WAL file
recycling logic used during normal operation works just as well during
archive recovery.

Per Fujii Masao's suggestion.

src/backend/access/transam/xlog.c

@@ -433,7 +433,6 @@ typedef struct XLogCtlData
 	 * recovery.  Protected by info_lck.
 	 */
 	bool		SharedRecoveryInProgress;
-	bool		SharedInArchiveRecovery;
 
 	/*
 	 * SharedHotStandbyActive indicates if we're still in crash or archive
@@ -620,7 +619,6 @@ static bool bgwriterLaunched = false;
 
 static void readRecoveryCommandFile(void);
 static void exitArchiveRecovery(TimeLineID endTLI, XLogSegNo endLogSegNo);
-static bool ArchiveRecoveryInProgress(void);
 static bool recoveryStopsHere(XLogRecord *record, bool *includeThis);
 static void recoveryPausesHere(void);
 static void SetLatestXTime(TimestampTz xtime);
@@ -2925,7 +2923,7 @@ RemoveOldXlogFiles(XLogSegNo segno, XLogRecPtr endptr)
 			strspn(xlde->d_name, "0123456789ABCDEF") == 24 &&
 			strcmp(xlde->d_name + 8, lastoff + 8) <= 0)
 		{
-			if (ArchiveRecoveryInProgress() || XLogArchiveCheckDone(xlde->d_name))
+			if (XLogArchiveCheckDone(xlde->d_name))
 			{
 				snprintf(path, MAXPGPATH, XLOGDIR "/%s", xlde->d_name);
 
@@ -3871,7 +3869,6 @@ XLOGShmemInit(void)
 	 */
 	XLogCtl->XLogCacheBlck = XLOGbuffers - 1;
 	XLogCtl->SharedRecoveryInProgress = true;
-	XLogCtl->SharedInArchiveRecovery = false;
 	XLogCtl->SharedHotStandbyActive = false;
 	XLogCtl->WalWriterSleeping = false;
 	XLogCtl->Insert.currpage = (XLogPageHeader) (XLogCtl->pages);
@@ -4265,7 +4262,6 @@ readRecoveryCommandFile(void)
 
 	/* Enable fetching from archive recovery area */
 	InArchiveRecovery = true;
-	XLogCtl->SharedInArchiveRecovery = true;
 
 	/*
 	 * If user specified recovery_target_timeline, validate it or compute the
@@ -4304,16 +4300,11 @@ exitArchiveRecovery(TimeLineID endTLI, XLogSegNo endLogSegNo)
 {
 	char		recoveryPath[MAXPGPATH];
 	char		xlogpath[MAXPGPATH];
-	/* use volatile pointer to prevent code rearrangement */
-	volatile XLogCtlData *xlogctl = XLogCtl;
 
 	/*
 	 * We are no longer in archive recovery state.
 	 */
 	InArchiveRecovery = false;
-	SpinLockAcquire(&xlogctl->info_lck);
-	xlogctl->SharedInArchiveRecovery = false;
-	SpinLockRelease(&xlogctl->info_lck);
 
 	/*
 	 * Update min recovery point one last time.
@@ -6110,25 +6101,6 @@ RecoveryInProgress(void)
 	}
 }
 
-/*
- * Are we currently in archive recovery? In the startup process, you can just
- * check InArchiveRecovery variable instead.
- */
-static bool
-ArchiveRecoveryInProgress()
-{
-	bool		result;
-	/* use volatile pointer to prevent code rearrangement */
-	volatile XLogCtlData *xlogctl = XLogCtl;
-
-	/* spinlock is essential on machines with weak memory ordering! */
-	SpinLockAcquire(&xlogctl->info_lck);
-	result = xlogctl->SharedInArchiveRecovery;
-	SpinLockRelease(&xlogctl->info_lck);
-
-	return result;
-}
-
 /*
  * Is HotStandby active yet? This is only important in special backends
  * since normal backends won't ever be able to connect until this returns