Clean up STF request_vc call

[Kailai-Wang]

Context

As topic.

We only use author_requestVc to send vc request, so both STF rust and ts part are removed.

It includes a bunch of clippy warning fixes too.

[linear]

P-963 Cleanup stf VC call

[jonalvarezz]

My only concern is that we will no longer able to use Polkadot.js App to request VCs, right?

However, since we are working on these series of playground tools, that part should be covered. so, nothing against merging.

[Kailai-Wang]

Yes it was discussed before - we have your sandbox :)

[felixfaisal]

LGTM