vote_deactivate: drop collateral gate, trust validator quorum

[LandynDev]

Summary

Remove the collateral >= min_collateral precondition from vote_deactivate so validator consensus alone is authoritative. The contract trusts the quorum — the threshold itself is the abuse protection, same envelope as vote_activate / vote_reserve.

Why

The original gate was designed to prevent validator collusion against compliant miners, but it narrows vote_deactivate to exactly one remediation case (min-raise cleanup). Removing it gives the validator layer freedom to invoke deactivation for any reason the quorum deems valid — min-raise, protocol abuse, operational emergencies — without needing a new on-chain gate per case.

Miner protection against malicious quorum unchanged in practice: the validator set is already trusted for reserve / initiate / confirm / slash paths. If the quorum is compromised, there are bigger problems than one extra deactivate vector.

Changes

• smart-contracts/ink/lib.rs — drop the if miner_collateral >= self.min_collateral { Err(SufficientCollateral) } check from vote_deactivate; keep the !miner_active → InvalidStatus guard.
• smart-contracts/ink/errors.rs — remove the now-unused SufficientCollateral variant.
• allways/contract_client.py — drop the variant from CONTRACT_ERROR_VARIANTS (renumbers HasActiveSwap from 29 → 28, CurrentlyReserved from 30 → 29). Update vote_deactivate client docstring.
• plans/scoring-simplification-and-contract-hardening.md — reflect the simplified semantics (local-only file, not in repo).

Follow-ups

• entrius/alw-utils PR for suite 21 already pushed: drops the above-floor rejection assertion.

Test plan

• cargo check — contract compiles
• pytest -q — 279 tests pass
• ruff check — clean
• Rebuild contract in dev env; E2E suite 21 passes (contract redeploy required because the error enum changed)