Remove "smgr_persistence == 0" dead code.

Reaching that code would have required multiple processes performing
relation extension during recovery, which does not happen.  That caller
has the persistence available, so pass it.  This was dead code as soon
as commit 210622c60e added it.

Discussion: https://postgr.es/m/CAN55FZ0JKL6vk1xQp6rfOXiNFV1u1H0tJDPPGHWoiO3ea2Wc=A@mail.gmail.com

src/backend/storage/buffer/bufmgr.c

@@ -1002,7 +1002,7 @@ ExtendBufferedRelTo(BufferManagerRelation bmr,
 	if (buffer == InvalidBuffer)
 	{
 		Assert(extended_by == 0);
-		buffer = ReadBuffer_common(bmr.rel, bmr.smgr, 0,
+		buffer = ReadBuffer_common(bmr.rel, bmr.smgr, bmr.relpersistence,
 								   fork, extend_to - 1, mode, strategy);
 	}
 
@@ -1117,16 +1117,8 @@ PinBufferForBlock(Relation rel,
 
 	Assert(blockNum != P_NEW);
 
-	/*
-	 * If there is no Relation it usually implies recovery and thus permanent,
-	 * but we take an argument because CreateAndCopyRelationData can reach us
-	 * with only an SMgrRelation for an unlogged relation that we don't want
-	 * to flag with BM_PERMANENT.
-	 */
 	if (rel)
 		persistence = rel->rd_rel->relpersistence;
-	else if (smgr_persistence == 0)
-		persistence = RELPERSISTENCE_PERMANENT;
 	else
 		persistence = smgr_persistence;
 

src/include/storage/bufmgr.h

@@ -114,14 +114,10 @@ typedef struct BufferManagerRelation
 
 struct ReadBuffersOperation
 {
-	/*
-	 * The following members should be set by the caller.  If only smgr is
-	 * provided without rel, then smgr_persistence can be set to override the
-	 * default assumption of RELPERSISTENCE_PERMANENT.
-	 */
-	Relation	rel;
+	/* The following members should be set by the caller. */
+	Relation	rel;			/* optional */
 	struct SMgrRelationData *smgr;
-	char		smgr_persistence;
+	char		smgr_persistence;	/* optional if rel != NULL */
 	ForkNumber	forknum;
 	BufferAccessStrategy strategy;