feat: Drop final active blessed version components

[Bownairo]

ReplicaVersionRecords and the blessed versions list are updated in sync, as we no longer require an extra proposal to have each version "blessed".

This removes the tracking of this list from the registry canister, and updates the last few components in sync. All uses have been cleared in this repo, and DRE tools have been updated as well.

What remains is cleaning up this record from the live registry, and a few miscellaneous followups.

[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?

How to Satisfy This Automatic Review

1. Go to the bottom of the pull request page.

2. Look for where it says this bot is requesting changes.

3. Click the three dots to the right.

4. Select "Dismiss review".

5. In the text entry box, respond to each of the numbered items in the previous
   section, declare one of the following:

• Done.

• $REASON_WHY_NO_NEED. E.g. for unreleased_changelog.md, "No
  canister behavior changes.", or for item 2, "Existing APIs
  behave as before.".

Brief Guide to "Externally Visible" Changes

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

Changes to EXISTING APIs are more likely to be "breaking".

If these changes are breaking, make sure that clients know how to migrate, how to
maintain their continuity of operations.

If your changes are behind a feature flag, then, do NOT add entrie(s) to
unreleased_changelog.md in this PR! But rather, add entrie(s) later, in the PR
that enables these changes in production.

Reference(s)

For a more comprehensive checklist, see here.

GOVERNANCE_CHECKLIST_REMINDER_DEDUP

[zeropath-ai]

✅ No security or compliance issues detected. Reviewed everything up to da50ffc.

Security Overview

• 🔎 Scanned files: 8 changed file(s)
• 🔗 Scan Link: https://zeropath.com/app/repositories/f975f1a5-0a47-4a3b-b7f0-a55609e90390?scanId=d642113a-e849-4fcc-be05-91852b6f368e&codeScanTypes=PrScan&tab=issues

Detected Code Changes

Change Type	Relevant files
Refactor	► rs/nns/integration_tests/src/registry_get_changes_since.rs     Adjust expected deltas length in integration tests ► rs/nns/integration_tests/src/upgrades_handler.rs     Update error messages in upgrade handler tests ► rs/nns/test_utils/src/registry.rs     Remove BlessedReplicaVersions from test utility ► rs/prep/src/bin/prep.rs     Update CLI help text to reflect changes ► rs/prep/src/internet_computer.rs     Remove BlessedReplicaVersions setup ► rs/registry/canister/src/mutations/do_revise_elected_replica_versions.rs     Remove logic related to blessed replica versions ► rs/registry/keys/src/lib.rs     Remove blessed_replica_versions key ► rs/test_utilities/registry/src/lib.rs     Remove add_blessed_replica_versions function
Bug Fix	► rs/nns/integration_tests/src/registry_get_changes_since.rs     Correct expected delta count in tests