Remove unused parameter for AcceptBlock

Summary: As per title. This param is a null or dummy parameter everywhere AcceptBlock is used.

Test Plan:

make check

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D2127