Remove canonical URLs from demo metadata

[Mandrenkov]

Title:
Remove the canonicalURL field from demo metadata.

Summary:
This PR removes the canonicalURL field from existing demo metadata. The canonicalURL field has been superseded by the (autogenerated) slug field as of #1228.

Relevant references:
None.

Possible Drawbacks:
None.

Related GitHub Issues:
None.

---

Detailed Changes:

1. Fixed the $id reference in demo.metadata.schema.0.1.3.json.
2. Added demo.metadata.schema.0.1.4.json which removes the canonicalURL field.
3. Updated the example metadata in demonstrations_metadata.md.
4. Removed the canonicalURL field from existing demo metadata (and adjusted dateOfLastModification).
5. Deleted the obsolete update_metadata.py script.

Merge Checklist:

• Delete the "Build Website - Text (Test)" GHA workflow which was added for testing purposes.

Verification:

The generated metadata.json file in the Glass Onion bucket no longer has any canonicalURL fields:

metadata.json Snippet

[
  {
    "authors": [
      {
        "username": "whatsis"
      }
    ],
    "basedOnPapers": [],
    "categories": [
      "Quantum Computing",
      "How-to"
    ],
    "dateOfLastModification": "2024-10-07T00:00:00+00:00",
    "dateOfPublication": "2024-10-01T00:00:00+00:00",
    "doi": "",
    "previewImages": [
      {
        "type": "thumbnail",
        "uri": "/_static/demo_thumbnails/regular_demo_thumbnails/thumbnail_how_to_use_noise_models.png"
      },
      {
        "type": "large_thumbnail",
        "uri": "/_static/demo_thumbnails/large_demo_thumbnails/thumbnail_large_how_to_use_noise_models.png"
      }
    ],
    "referencedByPapers": [],
    "references": [],
    "relatedContent": [
      {
        "id": "tutorial_noisy_circuits",
        "type": "demonstration",
        "weight": 1
      }
    ],
    "seoDescription": "Learn how noise models can be built and inserted into a quantum circuit in PennyLane.",
    "slug": "tutorial_how_to_use_noise_models",
    "tags": [],
    "title": "How to use noise models in PennyLane"
  },
  ...
]

[github-actions]

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Deployment Info:

• Pull Request ID: 1232
• Deployment SHA: 8ff896c72cca3a2526551e45491d829e67fbe68a
  (The Deployment SHA refers to the latest commit hash the docs were built from)

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[doctorperceptron]

LGTM

[anthayes92]

Looks good with TODOs ⭐ One question about version number