Update chainparams for 0.19.6 release
Update chainparams for 0.19.6 release

Summary: Per release process. Testnet skipped due to continued reorgs.

Test Plan:
  make check
Compare against your own node

Reviewers: #bitcoin_abc, deadalnix, jasonbcox, Mengerian

Reviewed By: #bitcoin_abc, deadalnix, jasonbcox, Mengerian

Subscribers: Mengerian

Differential Revision: https://reviews.bitcoinabc.org/D3051

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