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

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

src/validation.h

@@ -595,6 +595,8 @@ protected:
     //! mempool that is kept in sync with the chain
     CTxMemPool& m_mempool;
 
+    const CChainParams& m_params;
+
     //! Manages the UTXO set, which is a reflection of the contents of `m_chain`.
     std::unique_ptr<CoinsViews> m_coins_views;