Remove redundant CChainParams from ConnectBlock

Summary: T166: Cleanup redudant code since config.GetChainParams() can be used in place of the CChainParams parameter.

Test Plan: make check

Reviewers: deadalnix, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1010