[refactor] remove const CChainParams& object from CWallet

Summary:
this replaces the const chainParams& member in CWallet with a public method that retrieves it from its Chain interface

the exception is the case of the Chain-less bitcoin-wallet/wallet-tool, where it returns the global Params(), which at least is in single place now instead of a billion.

Test Plan:

ninja check check-functional

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D7041