[backport#16898] test: Remove unused connect_nodes_bi
Summary:
https://github.com/bitcoin/bitcoin/pull/16898/commits/fadfd844de8c53034a97dfa6f771ffe9f523fba2
Depends on D6492
Concludes backport of Core PR16898
Test Plan:
ninja check-all
Reviewers: #bitcoin_abc, jasonbcox
Reviewed By: #bitcoin_abc, jasonbcox
Differential Revision: https://reviews.bitcoinabc.org/D6493