Merge #13743: refactor: Replace boost::bind with std::bind

cb53b825c2 scripted-diff: Replace boost::bind with std::bind (Chun Kuan Lee)
2196c51821 refactor: Use boost::scoped_connection in signal/slot, also prefer range-based loop instead of std::transform (Chun Kuan Lee)

Pull request description:

  Replace boost::bind with std::bind

  - In `src/rpc/server.cpp`, replace `std::transform` with simple loop.
  - In `src/validation.cpp`, store the `boost::signals2::connection` object and use it to disconnect.
  - In `src/validationinterface.cpp`, use 2 map to store the `boost::signals2::scoped_connection` object.

Tree-SHA512: 6653cbe00036fecfc495340618efcba6d7be0227c752b37b81a27184433330f817e8de9257774e9b35828026cb55f11ee7f17d6c388aebe22c4a3df13b5092f0

src/test/test_bitcoin.cpp

@@ -89,7 +89,7 @@ TestingSetup::TestingSetup(const std::string& chainName) : BasicTestingSetup(cha
 
         // We have to run a scheduler thread to prevent ActivateBestChain
         // from blocking due to queue overrun.
-        threadGroup.create_thread(boost::bind(&CScheduler::serviceQueue, &scheduler));
+        threadGroup.create_thread(std::bind(&CScheduler::serviceQueue, &scheduler));
         GetMainSignals().RegisterBackgroundSignalScheduler(scheduler);
 
         mempool.setSanityCheck(1.0);