Merge #21016: refactor: remove boost::thread_group usage

dc8be12510 refactor: remove boost::thread_group usage (fanquake)

Pull request description:

  Post #18710, there isn't much left using `boost::thread_group`, so should just be able to replace it with the standard library. This also removes the last use of `boost::thread_interrupted`.

  After this change, last piece of Boost Thread we'd be using is `boost::shared_mutex`. See the commentary [here](https://github.com/bitcoin/bitcoin/issues/16684#issuecomment-726214696) as to why it may be non-trivial to swap that for `std::shared_mutex` in the near future.

  Closes #17307

ACKs for top commit:
  laanwj:
    Code review re-ACK dc8be12510
  MarcoFalke:
    review ACK dc8be12510 🔁
  jonatack:
    Non-expert code review ACK dc8be12510, also checked range-diff since last review and that local debug build is clean with gcc 10.2.1-6 on Debian

Tree-SHA512: 5510e2d760cce824234207dc86b1551ca8f21cbf3a2ce753c0254a0d03ffd83c94e449aec202fb7bd76e6fc64df783a6b70a736b0add9ece3734bb9c8ce8fc2f

test/lint/lint-includes.sh

@@ -67,9 +67,8 @@ EXPECTED_BOOST_INCLUDES=(
     boost/signals2/optional_last_value.hpp
     boost/signals2/signal.hpp
     boost/test/unit_test.hpp
-    boost/thread/condition_variable.hpp
+    boost/thread/lock_types.hpp
     boost/thread/shared_mutex.hpp
-    boost/thread/thread.hpp
 )
 
 for BOOST_INCLUDE in $(git grep '^#include <boost/' -- "*.cpp" "*.h" | cut -f2 -d: | cut -f2 -d'<' | cut -f1 -d'>' | sort -u); do