samples: net: lwm2m_client: Remove nrf52dk_nrf52832 from the allowlist

BLE and LwM2M grew in terms of RAM usage so that the sample does not
fit into nRF52832 anymore in the default configuration. This cause
twister to report an error when overflows errors are enabled.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>