is there a reason for unregprod to leave the entry

[ericpassmore]

Transferred from AntelopeIO/reference-contracts#5 original author cc32d9

unregprod marks an entry in producer_info as inactive and erases the key, instead of deleting it.

As a result, the table only grows and consumes the memory without a need.

is anything preventing us from deleting the entry on unreg?