DDF-4975 Remove Describe Endpoint from Catalog ThreatModel

[tyler30clemens]

What does this PR do?

The Describe Endpoint has been approved for deprecation. This PR removes those references from the Catalog.json ThreatModel. It also cleans up the ThreatModel by removing a now unused boundary, along with a now floating and disconnected External Describe Service actor value in the threat model.

Who is reviewing it?

@austinsteffes
@ahoffer
@bakejeyner

Select relevant component teams:

@codice/security

Ask 2 committers to review/merge the PR and tag them here.

@brjeter
@stustison
@blen-desta

How should this be tested?

Use a service such as OWASP Threat Dragon to view the Catalog.json threat model. Verify it all looks good and there are no references to the Describe Endpoint. See screenshot for how it should look.

What are the relevant tickets?

Fixes: #4975

Screenshots

Checklist:

• Documentation Updated
• Update / Add Threat Dragon models
• Update / Add Unit Tests
• Update / Add Integration Tests

Notes on Review Process

Please see Notes on Review Process for further guidance on requirements for merging and abbreviated reviews.

Review Comment Legend:

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• ❗ (Exclamation Mark) This comment is critical and requires clarification or action before approval.

[brjeter]

Hero successful ✅

[brjeter]

Merging without CI as this change cannot affect the build.