Revert "[chronik] Electrum: add the blockchain.headers.subscribe endpoint"
Summary:
This reverts commit rABC9b02451660e2d4aa2b1394a4ece44e58981bb494.
There is a subtle difference in the notification format vs Fulcrum that I missed, this needs to be fixed.
Test Plan:
ninja all check-all
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Differential Revision: https://reviews.bitcoinabc.org/D18077