Remove dead assignment to local variable.

This should have been removed in commit 7e30c186da, which split the loop
into two. Only the first loop uses the 'from' variable; updating it in
the second loop is bogus. It was never read after the first loop, so this
was harmless and surely optimized away by the compiler, but let's be tidy.

Backpatch to all supported versions.

Author: Ranier Vilela
Discussion: https://www.postgresql.org/message-id/CAEudQAoWq%2BAL3BnELHu7gms2GN07k-np6yLbukGaxJ1vY-zeiQ%40mail.gmail.com

src/backend/access/nbtree/nbtxlog.c

@@ -75,7 +75,6 @@ _bt_restore_page(Page page, char *from, int len)
 		if (PageAddItem(page, items[i], itemsizes[i], nitems - i,
 						false, false) == InvalidOffsetNumber)
 			elog(PANIC, "_bt_restore_page: cannot add item to page");
-		from += itemsz;
 	}
 }