Remove senate dead code

[Mahdi3Bani]

The senate/Triumvirate pallet was removed from the subtensor runtime, but the Python SDK still contained orphaned code querying it.

• Remove get_vote_data() from sync and async subtensor clients
• Delete ProposalVoteData dataclass and its module
• Remove get_vote_data from Chain API wrapper
• Remove all public exports of ProposalVoteData
• Remove unit tests for the dead method
• Remove commented-out senate e2e tests and dead imports
• Remove orphaned propose/vote test helpers

Fixes #3282

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Description of the Change

The Senate/Triumvirate pallet was removed from the subtensor runtime, but the Python SDK still contained orphaned code with TODO comments acknowledging the deprecation (e.g., # TODO: is this all deprecated? Didn't subtensor senate stuff get removed?). This PR completes the cleanup by removing all dead Senate/Triumvirate code across 9 files (499 lines deleted). Deprecated proxy enum values (Triumvirate, Senate, Governance, RootWeights) were intentionally kept as they may still be needed for deserializing existing on-chain proxy data.

Alternate Designs

N/A — This is straightforward dead code removal. The only design decision was whether to also remove the deprecated proxy enum values in proxy.py. These were kept to avoid breaking deserialization of existing on-chain proxy records.

Possible Drawbacks

None. The Triumvirate pallet no longer exists on-chain, so get_vote_data() already silently returned None or errored. No working functionality is affected.

Verification Process

• Searched the entire codebase for any remaining references to ProposalVoteData, get_vote_data, and proposal_vote_data — zero matches remain
• Verified all removed test helpers (propose, async_propose, vote, async_vote) were only used in the commented-out senate tests
• Verified the ProposalVoteData import was not used anywhere outside the deleted code paths

Release Notes

Removed deprecated Senate/Triumvirate dead code from the SDK (get_vote_data, ProposalVoteData, and related test code).

Branch Acknowledgement

[x] I am acknowledging that I am opening this branch against master

[thewhaleking]

See: #3283 (comment)