[refactor] Make MainSignals RAII styled

src/bitcoin-chainstate.cpp

@@ -74,13 +74,11 @@ int main(int argc, char* argv[])
     // Start the lightweight task scheduler thread
     scheduler.m_service_thread = std::thread(util::TraceThread, "scheduler", [&] { scheduler.serviceQueue(); });
 
-    CMainSignals validation_signals{};
+    CMainSignals validation_signals{scheduler};
 
     // Gather some entropy once per minute.
     scheduler.scheduleEvery(RandAddPeriodic, std::chrono::minutes{1});
 
-    validation_signals.RegisterBackgroundSignalScheduler(scheduler);
-
     class KernelNotifications : public kernel::Notifications
     {
     public:
@@ -303,5 +301,4 @@ epilogue:
             }
         }
     }
-    validation_signals.UnregisterBackgroundSignalScheduler();
 }