refactor: Remove call to StartShutdown from stop RPC

Use SignalInterrupt object instead. There is a slight change in behavior here
because the previous StartShutdown code used to abort on failure and the
new code returns an RPC error instead.

Author: ryanofsky

src/rpc/server.cpp

@@ -8,9 +8,11 @@
 #include <common/args.h>
 #include <common/system.h>
 #include <logging.h>
+#include <node/context.h>
+#include <rpc/server_util.h>
 #include <rpc/util.h>
-#include <shutdown.h>
 #include <sync.h>
+#include <util/signalinterrupt.h>
 #include <util/strencodings.h>
 #include <util/string.h>
 #include <util/time.h>
@@ -179,7 +181,7 @@ static RPCHelpMan stop()
 {
     // Event loop will exit after current HTTP requests have been handled, so
     // this reply will get back to the client.
-    StartShutdown();
+    CHECK_NONFATAL((*CHECK_NONFATAL(EnsureAnyNodeContext(jsonRequest.context).shutdown))());
     if (jsonRequest.params[0].isNum()) {
         UninterruptibleSleep(std::chrono::milliseconds{jsonRequest.params[0].getInt<int>()});
     }