Reduce externs

src/contest_link_80F57C4.c

@@ -39,6 +39,7 @@
 #include "constants/rgb.h"
 #include "constants/songs.h"
 #include "constants/vars.h"
+#include "contest.h"
 
 struct ContestLinkUnk0
 {
@@ -99,8 +100,6 @@ extern const struct SpriteSheet gUnknown_0858D810[];
 extern const struct SpritePalette gUnknown_0858D850;
 extern const struct SpriteTemplate gSpriteTemplate_858D860;
 
-extern void sub_81D9DE4(u8);
-
 static void sub_80F6A9C(void);
 static void sub_80F71C8(void);
 u8 sub_80F7310(u8, u8);