Transformers: Remove formatString feature toggle (#113756)

* Transformers: Remove formatString feature toggle

The formatString feature toggle was in GA stage and enabled by default.
This change removes the feature toggle and makes the format string
transformer always available.

Changes:
- Remove formatString feature toggle definition from registry
- Remove conditional check in standardTransformers.ts
- Update feature toggle git log with deletion timestamp
- Regenerate feature toggle files

* fix lint errors

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

@@ -242,11 +242,6 @@ export interface FeatureToggles {
   */
   disableClassicHTTPHistogram?: boolean;
   /**
-  * Enable format string transformer
-  * @default true
-  */
-  formatString?: boolean;
-  /**
   * Routes snapshot requests from /api to the /apis endpoint
   */
   kubernetesSnapshots?: boolean;