reset neuron data on dereg

[andreea-popescu-reef]

reviving: https://github.com/opentensor/subtensor/pull/522

Description

On neuron registration the trust, emission, consensus, incentive, dividends values as well as axon info associated with the assigned neuron_uid are inherited from the previous neuron. Thus for the first few blocks after registration these values will be wrong, then reset to zero and then get populated with the correct values for the newly registered neuron. This change resets these values on neuron registration.