log: remove increasing windows usage in fastpath The purpose of increasing windows is to allow backwards iteration on the filelog at a reasonable cost. But is it needed? - if follow is False, we have no reason to iterate backwards. We basically just want to walk the complete filelog and yield all revisions within the revision range. We can do this forward or backwards, as it only reads the index. - when follow is True, we need to examine the contents of the filelog, and to do this efficiently we need to read the filelog forward. And on the other hand, to track ancestors and copies, we need to process revisions backwards. But is it necessary to use increasing windows for this? We can iterate over the complete filelog forward, stack the revisions, and read the reversed(pile), it does the same thing with a more readable code.