remove unused mp_board_init() and board_gc_collect() per review comments

Author: dhalbert

main.c

@@ -207,9 +207,6 @@ static void start_mp(safe_mode_t safe_mode) {
 
     // Always return to root
     common_hal_os_chdir("/");
-
-    // Initialization for individual boards when a VM starts.
-    mp_board_init();
 }
 
 static void stop_mp(void) {
@@ -1152,7 +1149,6 @@ void gc_collect(void) {
     gc_collect_root((void **)&MP_STATE_VM(vfs_mount_table), sizeof(mp_vfs_mount_t) / sizeof(mp_uint_t));
 
     port_gc_collect();
-    board_gc_collect();
 
     background_callback_gc_collect();
 

supervisor/board.h

@@ -25,10 +25,3 @@ void reset_board(void);
 // state. It should not prevent the user access method from working (such as
 // disabling USB, BLE or flash) because CircuitPython may continue to run.
 void board_deinit(void);
-
-// Initialization for individual boards when a VM starts.
-void mp_board_init(void);
-
-// Some boards may want to mark additional pointers as gc roots.
-// A default weak implementation is provided that does nothing.
-void board_gc_collect(void);

supervisor/shared/board.c

@@ -44,11 +44,3 @@ MP_WEAK void board_deinit(void) {
 // Do-nothing so not all boards need to provide this function.
 MP_WEAK void reset_board(void) {
 }
-
-// Do-nothing so not all boards need to provide this function.
-MP_WEAK void mp_board_init(void) {
-}
-
-// Do-nothing so not all boards need to provide this function.
-MP_WEAK void board_gc_collect(void) {
-}