Remove deprecated GitHub Spark articles and redirect to changelog (#62994)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: SiaraMist <108543037+SiaraMist@users.noreply.github.com>
Co-authored-by: sunbrye <sunbrye@github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: aeec401b-5cf5-450d-a216-774f0f0e168e

Author: 4 people

content/billing/concepts/product-billing/github-spark.md

@@ -16,7 +16,6 @@ children:
   - /github-packages
   - /cloud-and-local-sandboxes
   - /git-lfs
-  - /github-spark
 contentType: concepts
 ---
 

content/billing/concepts/product-billing/index.md

@@ -9,7 +9,6 @@ children:
   - /chat
   - /agents
   - /about-cloud-and-local-sandboxes
-  - /spark
   - /copilot-usage-metrics
   - /prompting
   - /context

content/copilot/concepts/index.md

@@ -9,7 +9,6 @@ children:
   - /manage-access
   - /manage-enterprise-policies
   - /manage-agents
-  - /manage-spark
   - /manage-availability-of-default-models
   - /enable-custom-models
   - /review-audit-logs

content/copilot/concepts/spark.md

@@ -10,7 +10,6 @@ children:
   - /view-logs
   - /troubleshoot-firewall-settings
   - /troubleshoot-network-errors
-  - /troubleshoot-spark
   - /troubleshoot-copilot-slowness
 redirect_from:
   - /copilot/troubleshooting-github-copilot