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/table/measurements.cpp b/daemon/table/measurements.cpp
index 8ab89cc..adfd782 100644
--- a/daemon/table/measurements.cpp
+++ b/daemon/table/measurements.cpp
@@ -27,6 +27,7 @@
 #include "name-tree.hpp"
 #include "pit-entry.hpp"
 #include "fib-entry.hpp"
+#include "daemon/global.hpp"
 
 namespace nfd {
 namespace measurements {
@@ -49,7 +50,7 @@
   entry = nte.getMeasurementsEntry();
 
   entry->m_expiry = time::steady_clock::now() + getInitialLifetime();
-  entry->m_cleanup = scheduler::schedule(getInitialLifetime(), [=] { cleanup(*entry); });
+  entry->m_cleanup = getScheduler().schedule(getInitialLifetime(), [=] { cleanup(*entry); });
 
   return *entry;
 }
@@ -133,9 +134,9 @@
     return;
   }
 
-  scheduler::cancel(entry.m_cleanup);
+  entry.m_cleanup.cancel();
   entry.m_expiry = expiry;
-  entry.m_cleanup = scheduler::schedule(lifetime, [&] { cleanup(entry); });
+  entry.m_cleanup = getScheduler().schedule(lifetime, [&] { cleanup(entry); });
 }
 
 void