Update chainparams for 0.19.7 release

Summary:
Per release process.
Testnet has been updated in D3149, no need to update it again.

Test Plan:

make check

Compare against your node

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D3171