[ion] Board: remove shutdown method

- It should shutdown the ExternalFlash
- But it cannot be done in one function because some code need to be
in the external flash and some other in the internal flash.

ion/src/device/shared/drivers/board.cpp

@@ -18,11 +18,6 @@ namespace Board {
 
 using namespace Regs;
 
-void shutdown() {
-  shutdownPeripherals();
-  shutdownClocks();
-}
-
 void initFPU() {
 // http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0553a/BABDBFBJ.html
   CORTEX.CPACR()->setAccess(10, CORTEX::CPACR::Access::Full);

ion/src/device/shared/drivers/board.h

@@ -6,7 +6,6 @@ namespace Device {
 namespace Board {
 
 void init();
-void shutdown();
 
 void initFPU();
 void initClocks();