Merge pull request #769 from TanekLiang/stm32l475-iot

[bsp] fixed scons building error and update mdk project

bsp/stm32l475-iot-disco/drivers/SConscript

@@ -7,7 +7,6 @@ cwd     = os.path.join(str(Dir('#')), 'drivers')
 # add the general drivers.
 src = Split("""
 board.c
-stm32l4xx_nucleo.c
 usart.c
 """)