Transforms: Extract Fields: Remove Deduplication feature toggle (#113709)

Remove extractFieldsNameDeduplication feature toggle

The extractFieldsNameDeduplication feature has reached GA (General Availability),
so the feature toggle is no longer needed. The name deduplication behavior is
now permanently enabled.

Changes:
- Removed feature toggle definition from registry.go
- Removed feature toggle check in extractFields.ts (always deduplicate now)
- Updated tests to remove feature toggle manipulation
- Regenerated feature toggle files

packages/grafana-data/src/types/featureToggles.gen.ts

@@ -363,10 +363,6 @@ export interface FeatureToggles {
   */
   annotationPermissionUpdate?: boolean;
   /**
-  * Make sure extracted field names are unique in the dataframe
-  */
-  extractFieldsNameDeduplication?: boolean;
-  /**
   * Enables dashboard rendering using Scenes for viewer roles
   * @default true
   */