> txindex: Remove unused boost/thread
> txdb: Remove unused boost/thread
> refactor: Specify boost/thread/thread.hpp explicitly
> There are predefined interruption points for boost::thread: https://www.boost.org/doc/libs/1_71_0/doc/html/thread/thread_management.html#interruption_points
>
> However, non-boost threads such as std::thread or the main() thread can obviously not be interrupted. So remove all unused boost/thread from methods that are never executed in a boost::thread.
>
> Most of them were accompanied by a ShutdownRequested anyway. So even if the current thread was a boost::thread, the interruption point would be redundant. (We only interrupt threads during shutdown)
To make it work for our codebase, I had to add an addition include in system.cpp and core_io_tests.cpp.
This is a backport of core#18758