system/PeriodClock: move to time/

src/mixer/Memento.hxx

@@ -3,7 +3,7 @@
 
 #pragma once
 
-#include "system/PeriodClock.hxx"
+#include "time/PeriodClock.hxx"
 
 class MultipleOutputs;
 class BufferedOutputStream;

src/output/Control.hxx

@@ -9,7 +9,7 @@
 #include "thread/Thread.hxx"
 #include "thread/Mutex.hxx"
 #include "thread/Cond.hxx"
-#include "system/PeriodClock.hxx"
+#include "time/PeriodClock.hxx"
 
 #include <cstdint>
 #include <exception>

src/output/plugins/AlsaOutputPlugin.cxx

@@ -15,7 +15,7 @@
 #include "../Error.hxx"
 #include "mixer/plugins/AlsaMixerPlugin.hxx"
 #include "pcm/Export.hxx"
-#include "system/PeriodClock.hxx"
+#include "time/PeriodClock.hxx"
 #include "thread/Mutex.hxx"
 #include "thread/Cond.hxx"
 #include "util/Manual.hxx"