Remove bip9 from getblockchaininfo RPC call

Summary:
As per title.

Depends on D1546

Test Plan: bitcoin-cli getblockchaininfo help

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1550