chore: CRP-2972 CRP-2973 Remove pre_signatures_to_create_in_advance registry migration an update invariants

[eichhorl]

Previously (before the introduction of VetKD), the ChainKeyConfigs pre_signatures_to_create_in_advance field was mandatory (and set to Some(0) for VetKD). However, this field doesn't make sense for VetKD, and was migrated to None in #8247.

The migration has been completed, therefore this PR removes the migration code from the registry's post-upgrade.

Additionally, we extend the registry invariants to ensure that:

• Keys that require pre-signatures have a non-zero pre_signatures_to_create_in_advance
• Keys that don't require pre-signatures have pre_signatures_to_create_in_advance set to None

Canbench improvements:

Only significant changes:
| status | name                           | calls |     ins |  ins Δ% | HI |  HI Δ% | SMI |  SMI Δ% |
|--------|--------------------------------|-------|---------|---------|----|--------|-----|---------|
|   -    | migrate_canisters_10_times_100 |       | 153.04M |  -2.13% |  0 |  0.00% |   0 |   0.00% |

ins = instructions, HI = heap_increase, SMI = stable_memory_increase, Δ% = percent change

[github-actions]

This pull request changes code owned by the Governance team. Therefore, make sure that
you have considered the following (for Governance-owned code):

1. Update unreleased_changelog.md (if there are behavior changes, even if they are
   non-breaking).

2. Are there BREAKING changes?

3. Is a data migration needed?

4. Security review?

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Brief Guide to "Externally Visible" Changes

"Externally visible behavior change" is very often due to some NEW canister API.

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Reference(s)

For a more comprehensive checklist, see here.

GOVERNANCE_CHECKLIST_REMINDER_DEDUP

1. Done.
2. No breaking changes.
3. No data migration needed.
4. No security review needed.