This returns main chain to ForkID of 0 after the May 2020
upgrade, and implements automatic replay protection for
the Nov 2020 upgrade.
The next upgrade time is precisely 184.0 days after the
phonon activation time, and is:
Sunday, November 15, 2020 12:00:00 PM UTC
For reference see last HF:
https://reviews.bitcoinabc.org/D3868