Before this change `--track-renames-strategy` was broken. The hashing
method it used could declare times that were very close together to be
different.
The time hash was discarded and instead we check the modification time
window on every hash match.
Provided that the user doesn't use `--track-renames-strategy` on a
huge number of identically sized files this will perform just fine.
See: https://forum.rclone.org/t/track-renames-strategy-modtime-doesnt-work/16992/5
fb06427c69