SIMD-0138: Deprecate legacy vote instructions

proposals/0138-deprecate-legacy-vote-instructions.md

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+---
+simd: '0138'
+title: Deprecate legacy vote instructions
+authors:
+  - Ashwin Sekar
+category: Standard
+type: Core
+status: Review
+created: 2024-04-09
+feature: (fill in with feature tracking issues once accepted)
+---
+
+## Summary
+
+Disables the legacy `Vote`, `UpdateVoteState` and `CompactUpdateVoteState`
+instruction variants.
+
+## Motivation
+
+These instructions are no longer sent by validator clients.
+It is cumbersome to support these old vote instructions and ensure parity.
+
+## Alternatives Considered
+
+None
+
+## New Terminology
+
+None
+
+## Detailed Design
+
+When the features:
+
+* `deprecate legacy vote instructions`, with key
+    `depVvnQ2UysGrhwdiwU42tCadZL8GcBb1i2GYhMopQv`
+* `enable tower sync vote instruction`, with key
+    `tSynMCspg4xFiCj1v3TDb4c7crMR5tSBhLz4sF7rrNA`
+
+are activated, the following instructions will result in an
+`InvalidInstructionData` error:
+
+* `Vote`
+* `VoteSwitch`
+* `UpdateVoteState`
+* `UpdateVoteStateSwitch`
+* `CompactUpdateVoteState`
+* `CompactUpdateVoteStateSwitch`
+
+Enabling `deprecate legacy vote instructions` without 
+`enable tower sync vote instruction` should have no effect.
+
+## Impact
+
+Sending transactions that include the mentioned instructions will fail.
+
+## Security Considerations
+
+None
+
+## Backwards Compatibility
+
+Incompatible