refactor: Remove ::Params() global from inside CChainState member functions

Summary:
It is confusing and verbose to repeatedly access the global when a
member variable can simply refer to it.

This is a backport of core#21789 [1/2]
https://github.com/bitcoin/bitcoin/pull/21789/commits/fa389471251f043ec25e7b01e59b37d3b921ce54

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12189