More minor isolated fixes (#1258)

* Fix reversed array access in z_boss_dodongo.c

* Remove useless return in z_en_encount2.c

* Remove some redundant externs or declarations

* Move some undefs to be performed as early as possible

* AudioOcarina_ResetStaffs -> AudioOcarina_ResetStaves

The plural appears to be staves for the music term

* Remove some uses of UNK_PTR

* Use NULL for pointers set to 0 in z_game_dlftbls.c

* Remove useless !! in z_en_tk.c

* Revert "AudioOcarina_ResetStaffs -> AudioOcarina_ResetStaves"

This reverts commit 1b7fe62408.

* Remove more redundant externs from PR suggestion

src/overlays/actors/ovl_Boss_Dodongo/z_boss_dodongo.c

@@ -55,7 +55,7 @@ static InitChainEntry sInitChain[] = {
 };
 
 void func_808C1190(s16* arg0, u8* arg1, s16 arg2) {
-    if (arg2[arg1] != 0) {
+    if (arg1[arg2] != 0) {
         arg0[arg2 / 2] = 0;
     }
 }