cleanup: Move tox_get_system out of the public API.

It's not released, yet, and this function is a pain. We don't want it
going forward.

auto_tests/tox_dispatch_test.c

@@ -10,6 +10,7 @@
 #include "../toxcore/tox.h"
 #include "../toxcore/tox_dispatch.h"
 #include "../toxcore/tox_events.h"
+#include "../toxcore/tox_private.h"
 #include "../toxcore/tox_unpack.h"
 #include "auto_test_support.h"
 #include "check_compat.h"

testing/fuzzing/protodump_reduce.cc

@@ -4,6 +4,7 @@
 #include "../../toxcore/tox.h"
 #include "../../toxcore/tox_dispatch.h"
 #include "../../toxcore/tox_events.h"
+#include "../../toxcore/tox_private.h"
 #include "fuzz_support.h"
 #include "fuzz_tox.h"
 

toxcore/tox.h

@@ -922,8 +922,6 @@ Tox *tox_new(const struct Tox_Options *options, Tox_Err_New *error);
  */
 void tox_kill(Tox *tox);
 
-const Tox_System *tox_get_system(Tox *tox);
-
 /**
  * @brief Calculates the number of bytes required to store the tox instance with
  *   tox_get_savedata.

toxcore/tox_private.h

@@ -31,6 +31,8 @@ Tox_System tox_default_system(void);
 void tox_lock(const Tox *tox);
 void tox_unlock(const Tox *tox);
 
+const Tox_System *tox_get_system(Tox *tox);
+
 /**
  * Set the callback for the `friend_lossy_packet` event for a specific packet ID.
  * Pass NULL to unset.