Revert "Always sync alert escalation attributes to incidents"

What does this MR do and why?

Reverts !84139 (merged) in line with !83159 (comment 904704277).

Related issue: #356215 (closed)

Screenshots or screen recordings

There are no UI changes. Screenshots represent verification flow.

Creating new alert	Creating new incident w/o flag enabled	Incident after enabling the flag

How to set up and validate locally

1. Disable the feature flag if enabled

   Feature.disable(:incident_escalations)

2. Create an incident from an alert in the UI
   1. https://docs.gitlab.com/ee/operations/incident_management/integrations.html#triggering-test-alerts (project > Settings > Monitor > Alerts, pick a name, set to active, skip to "Save")
      1. Sample payload { "title": "Creating an incident from an alert" }
   2. Open alert list under project > Monitor > Alerts & click the recent row to open alert details
   3. Click 'Create Incident` (or open the associated incident if it was auto-created)
3. Check that an IncidentManagement::IssuableEscalationStatus record wasn't created by enabling the feature flag & refreshing the page/restart gdk (you should see None for the Status/Escalation policy fields)

   Feature.enable(:incident_escalations)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.