samples: stm32 power mngt enters low power
samples: stm32 power mngt enters low power

Remove this line because the pm_device_busy_set function will
prevent the system to enter low power.
This sample application wants to.

Signed-off-by: Francois Ramu <b83adc7f8a23ee911a37fcb61c4033581aae0b7a@st.com>

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