test: Remove unused cs_main
Summary:
This is a partial backport of core#25648
https://github.com/bitcoin/bitcoin/pull/25648/commits/fa7a9114e59b81b50584311a4ab2b3e9a8d956bd
Depends on D15753
Test Plan:
With Debug and tsan
ninja check
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D15754