Chainparams: Use name constants in chainparams initialization
Chainparams: Use name constants in chainparams initialization

Summary: This is a backport of Core [[https://github.com/bitcoin/bitcoin/pull/17306/files | PR17306]]

Test Plan:
  make check

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D5132

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