move #include "rgb.h" from quantum.h to quantum.c

I think `quantum.h` should contain only API declarations that `quantum.c` provides externally. `rgb.h` contains function weak definitions. This should not be in `quantum.h`.

quantum/quantum.c

@@ -15,6 +15,11 @@
  */
 
 #include "quantum.h"
+
+#if !defined(RGBLIGHT_ENABLE) && !defined(RGB_MATRIX_ENABLE)
+	#include "rgb.h"
+#endif
+
 #ifdef PROTOCOL_LUFA
 #include "outputselect.h"
 #endif