Remove deadcode

src/color.h

@@ -31,11 +31,4 @@ Color color_invert(Color c);
 
 Color color_scale(Color c, Color fc);
 
-static inline
-Color color_set_alpha(Color c, float a)
-{
-    c.a = a;
-    return c;
-}
-
 #endif  // COLOR_H_