cmd/bootdb: don't create genesis block
cmd/bootdb: don't create genesis block

bootdb was generating invalid genesis block headers. The API server will
auto-generate the genesis block, so it is not even necessary to do it in
bootdb.

Closes chain/chainprv#516.
Reviewers: da39a3ee5e6b4b0d3255bfef95601890afd80709@erykwalder

chain/chain,chain/chain,chain/chain,chain/chain,chain/chain,chain/chain