Remove redundant author requirement

[4meta5]

What does it do?

Removes panic in on_finalize if Author storage item isn't set. The requirement should still be enforced by the fact that the inherent which sets this storage item is required to be included in every block afaik paritytech/substrate#8002

I moved Author::kill() to on_initialize so that every block is finalized with the author set (assuming the inherent requirement enforces setting it correctly). I think this is better than clearing the author storage item before the block is finalized.

What important points reviewers should know?

Is there something left for follow-up PRs?

What alternative implementations were considered?

Are there relevant PRs or issues in other repositories (Substrate, Polkadot, Frontier, Cumulus)?

What value does it bring to the blockchain users?

Checklist

• Does it require a purge of the network? No
• You bumped the runtime version if there are breaking changes in the runtime ?
• Does it require changes in documentation/tutorials ? No

[JoshOrndorff]

Thanks!

Still needs a spec version bump.