core+daemon: eliminate scheduler::{schedule,cancel} wrappers

Also move core/global-io.hpp to daemon/global.hpp

Refs: #4528, #4883
Change-Id: I0b99029f1a19d7451aab57099cd3303b7eb42ff3
diff --git a/daemon/face/unicast-udp-transport.cpp b/daemon/face/unicast-udp-transport.cpp
index 062c924..c872c09 100644
--- a/daemon/face/unicast-udp-transport.cpp
+++ b/daemon/face/unicast-udp-transport.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2018,  Regents of the University of California,
+ * Copyright (c) 2014-2019,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -25,6 +25,7 @@
 
 #include "unicast-udp-transport.hpp"
 #include "udp-protocol.hpp"
+#include "daemon/global.hpp"
 
 #ifdef __linux__
 #include <cerrno>       // for errno
@@ -109,7 +110,7 @@
 void
 UnicastUdpTransport::scheduleClosureWhenIdle()
 {
-  m_closeIfIdleEvent = scheduler::schedule(m_idleTimeout, [this] {
+  m_closeIfIdleEvent = getScheduler().schedule(m_idleTimeout, [this] {
     if (!hasRecentlyReceived()) {
       NFD_LOG_FACE_INFO("Closing due to inactivity");
       this->close();