core: annotate Reexecute() as NoReply

So we're able to tell from the introspection data that the method
doesn't reply.

man/org.freedesktop.systemd1.xml

@@ -164,6 +164,7 @@ node /org/freedesktop/systemd1 {
       Dump(out s output);
       DumpByFileDescriptor(out h fd);
       Reload();
+      @org.freedesktop.DBus.Method.NoReply("true")
       Reexecute();
       @org.freedesktop.systemd1.Privileged("true")
       Exit();

src/core/dbus-manager.c

@@ -3083,7 +3083,7 @@ const sd_bus_vtable bus_manager_vtable[] = {
                       NULL,
                       NULL,
                       method_reexecute,
-                      SD_BUS_VTABLE_UNPRIVILEGED),
+                      SD_BUS_VTABLE_UNPRIVILEGED|SD_BUS_VTABLE_METHOD_NO_REPLY),
         SD_BUS_METHOD("Exit",
                       NULL,
                       NULL,