refactor: Drop boost::thread stuff in CCheckQueue

Summary:
This is a backport of core#18710 [4/4]
https://github.com/bitcoin/bitcoin/pull/18710/commits/bb6fcc75d1ec94b733d1477c816351c50be5faf9

Depends on D10987

Test Plan:
With TSAN: ninja && ninja check check-functional

cmake .. -GNinja -DCMAKE_BUILD_TYPE=Debug -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10988