Move OpenVR init function out of Overlaycontroller

This prevents the issue of OpenVR not being initialized in constructors
of other objects, and there's really no reason not to do it.

src/overlaycontroller.h

@@ -106,11 +106,6 @@ private:
     uint64_t m_lastFrame = 0;
     int m_vsyncTooLateCounter = 0;
 
-    // OpenVR_Init must be declared before any other class that uses OpenVR
-    // function calls since objects are initialized in order of declaration in
-    // the class.
-    openvr_init::OpenVR_Init m_openVrInit;
-
     input::SteamIVRInput m_actions;
 
 public: // I know it's an ugly hack to make them public to enable external