Creation of single commit should after minCertifyHeight

[shuse2]

Expected behavior

Node should not create unnecessary single commits

Actual behavior

Even though the created single commits will not be aggregated until minCertifyHeight, they are created and broadcasted to the network.
Especially, in the init phase, the BLS key will not registered on test/mainnet it will show Validator does not have registered BLS key.

Steps to reproduce

Run testnet node before the init phase as a validator

Which version(s) does this affect? (Environment, OS, etc...)

6.0.0-rc.2