vote: deprecate legacy vote instructions

[AshwinSekar]

Problem

Validator no longer sends the legacy vote instructions. It is cumbersome to keep these old vote instructions around and ensure parity.

Summary of Changes

Gate behind a new flag and the activation flag of the latest vote ix (TowerSync #365).
Once both of these are activated, legacy vote ixs will no longer be processed by the vote program.

For reviewers:

1st commit is the actual logic, second commit updates the tests.

Part of the #2597 effort

[lheeger-jump]

Needs SIMD. Can fast track.

Languages is very simple:

After feature gate, these instructions (list them) will no longer be supported.

[AshwinSekar]

solana-foundation/solana-improvement-documents#138

[mergify]

The Firedancer team maintains a line-for-line reimplementation of the
native programs, and until native programs are moved to BPF, those
implementations must exactly match their Agave counterparts.
If this PR represents a change to a native program implementation (not
tests), please include a reviewer from the Firedancer team. And please
keep refactors to a minimum.

[mergify]

If this PR represents a change to the public RPC API:

1. Make sure it includes a complementary update to rpc-client/ (example)
2. Open a follow-up PR to update the JavaScript client @solana/web3.js (example)

Thank you for keeping the RPC clients in sync with the server API @AshwinSekar.

[lidatong]

will impl on our side after bp