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/libultra/io/visetevent.c

@@ -1,7 +1,5 @@
 #include "global.h"
 
-extern OSViContext* __osViNext;
-
 void osViSetEvent(OSMesgQueue* mq, OSMesg msg, u32 retraceCount) {
     register u32 prevInt = __osDisableInt();