Remove unnecessary intersectRect() function

This function checked the intersection of rectangles, but it used floats
for some reason when its only caller used ints. There's already an
intersection function (UtilityClass::intersects()), so we should be
using that one instead in order to minimize code duplication.

Graphics::Hitest() is used for per-pixel collision detection, directly
checking the pixels of both entities' sprites. I checked with one of my
TASes and it still syncs, so I'm pretty sure this won't cause any
issues.

desktop_version/src/GraphicsUtil.h

@@ -39,8 +39,6 @@ void FillRect( SDL_Surface* surface, SDL_Rect& rect, const int r, int g, int b )
 
 void FillRect( SDL_Surface* surface, SDL_Rect rect, int rgba );
 
-bool intersectRect(float left1, float right1, float bottom1, float top1, float left2, float right2, float bottom2, float top2);
-
 void OverlaySurfaceKeyed(SDL_Surface* _src, SDL_Surface* _dest, Uint32 _key);
 
 void ScrollSurface(SDL_Surface* _src, int pX, int py);