Remove dead checks for invalid left page in ginDeletePage.

In some places, the function assumes the left page is valid, and in others,
it checks if it is valid. Remove all the checks.

src/backend/access/gin/ginvacuum.c

@@ -285,8 +285,7 @@ ginDeletePage(GinVacuumState *gvs, BlockNumber deleteBlkno, BlockNumber leftBlkn
 	GinPageGetOpaque(page)->flags = GIN_DELETED;
 
 	MarkBufferDirty(pBuffer);
-	if (leftBlkno != InvalidBlockNumber)
-		MarkBufferDirty(lBuffer);
+	MarkBufferDirty(lBuffer);
 	MarkBufferDirty(dBuffer);
 
 	if (RelationNeedsWAL(gvs->index))
@@ -294,7 +293,6 @@ ginDeletePage(GinVacuumState *gvs, BlockNumber deleteBlkno, BlockNumber leftBlkn
 		XLogRecPtr	recptr;
 		XLogRecData rdata[4];
 		ginxlogDeletePage data;
-		int			n;
 
 		data.node = gvs->index->rd_node;
 		data.blkno = deleteBlkno;
@@ -315,32 +313,22 @@ ginDeletePage(GinVacuumState *gvs, BlockNumber deleteBlkno, BlockNumber leftBlkn
 		rdata[1].len = 0;
 		rdata[1].next = rdata + 2;
 
-		if (leftBlkno != InvalidBlockNumber)
-		{
-			rdata[2].buffer = lBuffer;
-			rdata[2].buffer_std = FALSE;
-			rdata[2].data = NULL;
-			rdata[2].len = 0;
-			rdata[2].next = rdata + 3;
-			n = 3;
-		}
-		else
-			n = 2;
+		rdata[2].buffer = lBuffer;
+		rdata[2].buffer_std = FALSE;
+		rdata[2].data = NULL;
+		rdata[2].len = 0;
+		rdata[2].next = rdata + 3;
 
-		rdata[n].buffer = InvalidBuffer;
-		rdata[n].buffer_std = FALSE;
-		rdata[n].len = sizeof(ginxlogDeletePage);
-		rdata[n].data = (char *) &data;
-		rdata[n].next = NULL;
+		rdata[3].buffer = InvalidBuffer;
+		rdata[3].buffer_std = FALSE;
+		rdata[3].len = sizeof(ginxlogDeletePage);
+		rdata[3].data = (char *) &data;
+		rdata[3].next = NULL;
 
 		recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_DELETE_PAGE, rdata);
 		PageSetLSN(page, recptr);
 		PageSetLSN(parentPage, recptr);
-		if (leftBlkno != InvalidBlockNumber)
-		{
-			page = BufferGetPage(lBuffer);
-			PageSetLSN(page, recptr);
-		}
+		PageSetLSN(BufferGetPage(lBuffer), recptr);
 	}
 
 	if (!isParentRoot)