Don't cut off existing delta chains if we are reusing deltas
The existing pack file may have chains longer than our current max
depth, such as if it is a historical pack and was generated with a
maximum chain depth >100. Cutting off the chains would create a
bigger pack file that we need to transmit, and it costs a lot more
CPU time to expand the delta object in order to recompress it whole,
because we couldn't copy it directly from the pack file.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>