blockchain_converter: delete blockchain on succesful exit
blockchain_converter: delete blockchain on succesful exit

While the dtor implementation does not actually do anything, other
paths do delete it, and the dtor might do someting later.

eiabea/bitmonero,eiabea/bitmonero,ranok/bitmonero,eiabea/bitmonero,eiabea/bitmonero,ranok/bitmonero,ranok/bitmonero,eiabea/bitmonero,eiabea/bitmonero,ranok/bitmonero,ranok/bitmonero,ranok/bitmonero