Remove Legacy Banking Stage

[apfitzge]

Problem

• In 2.1, we added a warning that thread-local-multi-iterator block-production method would be deprecated (Deprecate Legacy BlockProductionMethod #3113)
• Now that we are on version 2.2, we should remove this variant from the BlockProductionMethod enum and remove supporting code

Proposed Solution

Likely this becomes a bit simpler once we also move forwarding to a separate stage: #3222
This may sound simple, but is not that simple to do in the best way. And I propose the following plan for removing the variant and the associated code:

• Remove BlockProductionMethod::ThreadLocalMultiIterator variant Remove the ThreadLocalMultiIterator BlockProductionMethod #3727
• Remove new_thread_local_multi_iterator Remove new_thread_local_multi_iterator #3757
• Remove UnprocessedTransactionStorage
  • we only ever need the VoteStorage variant now
  • remove ThreadLocalUnprocessedPackets
  • remove multi_iterator_scanner.rs
• Remove ImmutableDeserializedPacket innefficiency from Voting Threads