Use (void) in prototypes instead of ().

Also, removed `__inline` from an extern function (why was it there?).
Also, moved one extern declaration to a header file. There are lots of
these that need to be moved, but one thing at a time.

src/notify.h

@@ -60,7 +60,7 @@ typedef enum _Flags {
 } Flags;
 
 int init_notify(int login_cooldown, int notification_timeout);
-void terminate_notify();
+void terminate_notify(void);
 
 int sound_notify(ToxWindow *self, Notification notif, uint64_t flags, int *id_indicator);
 int sound_notify2(ToxWindow *self, Notification notif, uint64_t flags, int id);