Remove IncreaseRealtimeTick

Not needed as modal progress windows no longer use _realtime_tick

src/debug.h

@@ -134,15 +134,6 @@ const char *GetLogPrefix();
 /** The real time in the game. */
 extern uint32 _realtime_tick;
 
-inline void IncreaseRealtimeTick(uint32 increase)
-{
-#if defined(__GNUC__) || defined(__clang__)
-	__atomic_add_fetch(&_realtime_tick, increase, __ATOMIC_RELAXED);
-#else
-	_realtime_tick += increase;
-#endif
-}
-
 void ClearDesyncMsgLog();
 void LogDesyncMsg(std::string msg);
 char *DumpDesyncMsgLog(char *buffer, const char *last);