Unexport getgridpoint

It's a method of entityclass even though it doesn't use anything on the
class and it's not used outside of Entity.cpp.

desktop_version/src/Entity.h

@@ -119,8 +119,6 @@ public:
 
     int checkactivity(void);
 
-    int getgridpoint(int t);
-
     bool checkplatform(const SDL_Rect& temprect, int* px, int* py);
 
     bool checkblocks(const SDL_Rect& temprect, float dx, float dy, int dr, bool skipdirblocks);