chore(nervous-system): Remove is_mission_70_voting_rewards_enabled flag

[jasonz-dfinity]

Summary

• Phase 1 (voting rewards / dissolve-delay bounds / 8YG bonus) landed on mainnet via feat(governance): Enable Mission 70 voting rewards changes. #9923 on 2026-04-23, so the is_mission_70_voting_rewards_enabled flag has served its purpose.
• Inline the enabled branch at every call site; drop the flag definition (ENABLE_MISSION_70_VOTING_REWARDS, is_mission_70_voting_rewards_enabled, temporarily_enable_*, temporarily_disable_*).
• Simplify tests that previously exercised both branches: drop the pre_mission_70 / _disabled cases; collapse _with_mission_70 wrappers into the underlying tests; rename MISSION_70_VOTING_REWARDS_ADJUSTMENT_FACTOR → VOTING_REWARDS_ADJUSTMENT_FACTOR (now a plain constant).

Out of scope (deliberately kept)

• MAX_DISSOLVE_DELAY_SECONDS_PRE_MISSION_70 is still referenced for legacy/migration code that operates on neurons whose stored dissolve delay reflects the pre-M70 max.
• VotingPowerEconomics::DEFAULT_NEURON_MINIMUM_DISSOLVE_DELAY_TO_VOTE_SECONDS (6 months) remains as a default / fallback used in many places; only the M70 branch was inlined.
• max_dissolve_delay_seconds() is now a function that just returns the post-M70 constant; further inlining can happen later.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR removes the is_mission_70_voting_rewards_enabled feature flag and permanently inlines the Mission 70 (“enabled”) behavior across NNS Governance. This simplifies the codebase now that Mission 70 Phase 1 has already been deployed to mainnet and the flag no longer serves as a rollout/rollback mechanism.

Changes:

• Removed the Mission 70 voting rewards flag and its temporary enable/disable test helpers.
• Inlined post–Mission 70 logic for reward pool scaling, dissolve-delay bonus, minimum dissolve delay to vote, and 8-year-gang bonus application.
• Simplified/updated tests by dropping pre-M70 branches and renaming the voting rewards adjustment constant.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
rs/nns/governance/tests/governance.rs	Removes flag-dependent assertions and hardcodes post-M70 expected values in integration tests.
rs/nns/governance/src/voting.rs	Deletes dual-branch tests and collapses reward-distribution expectations to the post-M70 behavior.
rs/nns/governance/src/reward/calculation.rs	Removes flag-gated reward scaling; renames and directly applies the adjustment factor; simplifies tests accordingly.
rs/nns/governance/src/neuron/voting_power.rs	Removes flag-gated dissolve-delay bonus formula; keeps the post-M70 quadratic multiplier unconditionally.
rs/nns/governance/src/neuron/voting_power_tests.rs	Drops pre-M70 test cases and keeps a single post-M70 dissolve-delay bonus test.
rs/nns/governance/src/neuron/types/tests.rs	Removes tests and setup that depended on toggling the Mission 70 flag.
rs/nns/governance/src/neuron/types.rs	Applies 8-year-gang bonus unconditionally (post-M70 behavior) and removes the flag check.
rs/nns/governance/src/neuron_store/voting_power.rs	Uses the Mission 70 minimum dissolve delay to vote as the default fallback unconditionally.
rs/nns/governance/src/neuron_store/metrics/tests.rs	Updates bucket expectations to fixed post-M70 values; removes flag-conditional logic.
rs/nns/governance/src/lib.rs	Removes the thread-local flag definition and exported flag accessor / temporary toggles.
rs/nns/governance/src/governance/tests/mod.rs	Removes now-unnecessary Mission 70 flag setup in upgrade/migration tests.
rs/nns/governance/src/governance.rs	Inlines post-M70 max dissolve delay and removes flag-guarding around related migrations/defaults.

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