Move easylogging++ include into necessary files

logging.h previously had logic to enable debug logging even on release
builds. This logic was moved to the QMAKE file, hence the logging.h file
is no longer necessary.

src/main.cpp

@@ -8,7 +8,7 @@
 #include <QStandardPaths>
 #include <openvr.h>
 #include <iostream>
-#include "logging.h"
+#include <easylogging++.h>
 
 INITIALIZE_EASYLOGGINGPP