Move tempstring off of Graphics, Game, and UtilityClass

Unlike, say, the scriptclass i/j/k stuff, these tempstrings are only
purely visual, and there's no known glitches to manipulate them anyway.
Thus I think it's safe to make this cleanup.

desktop_version/src/UtilityClass.h

@@ -39,7 +39,6 @@ public:
     int globaltemp;
     int temp;
     int temp2;
-    std::string tempstring;
     std::vector<int> splitseconds;
 };