platform defines: Remove extraneous export macro.

Author: rpavlik

include/openxr/openxr_platform_defines.h

@@ -36,11 +36,7 @@ extern "C" {
  * Function pointer type: typedef void (XRAPI_PTR *PFN_xrFunction)(void);
  */
 #if defined(_WIN32)
-#ifdef XRAPI_DLL_EXPORT
-#define XRAPI_ATTR __declspec(dllexport)
-#else
 #define XRAPI_ATTR
-#endif
 // On Windows, functions use the stdcall convention
 #define XRAPI_CALL __stdcall
 #define XRAPI_PTR XRAPI_CALL