[STM32F0] Make device.h a common file

Author: Laurent MEUNIER

hal/targets/hal/TARGET_STM/TARGET_STM32F0/TARGET_DISCO_F051R8/device.h

@@ -32,22 +32,9 @@
 #ifndef MBED_DEVICE_H
 #define MBED_DEVICE_H
 
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 //=======================================
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 #define DEVICE_ID_LENGTH       24
 
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 #include "objects.h"
 
 #endif