chore(oidc): remove legacy storage methods (#10061)

# Which Problems Are Solved

Stabilize the optimized introspection code and cleanup unused code.

# How the Problems Are Solved

- `oidc_legacy_introspection` feature flag is removed and reserved.
- `OPStorage` which are no longer needed have their bodies removed.
- The method definitions need to remain in place so the interface
remains implemented.
  - A panic is thrown in case any such method is still called

# Additional Changes

- A number of `OPStorage` methods related to token creation were already
unused. These are also cleaned up.

# Additional Context

- Closes #10027 
- #7822

---------

Co-authored-by: Livio Spring <livio.a@gmail.com>

internal/query/system_features_model.go

@@ -57,7 +57,6 @@ func (m *SystemFeaturesReadModel) Query() *eventstore.SearchQueryBuilder {
 			feature_v2.SystemResetEventType,
 			feature_v2.SystemLoginDefaultOrgEventType,
 			feature_v2.SystemTriggerIntrospectionProjectionsEventType,
-			feature_v2.SystemLegacyIntrospectionEventType,
 			feature_v2.SystemUserSchemaEventType,
 			feature_v2.SystemTokenExchangeEventType,
 			feature_v2.SystemImprovedPerformanceEventType,
@@ -81,15 +80,12 @@ func reduceSystemFeatureSet[T any](features *SystemFeatures, event *feature_v2.S
 		return err
 	}
 	switch key {
-	case feature.KeyUnspecified,
-		feature.KeyActionsDeprecated:
+	case feature.KeyUnspecified:
 		return nil
 	case feature.KeyLoginDefaultOrg:
 		features.LoginDefaultOrg.set(level, event.Value)
 	case feature.KeyTriggerIntrospectionProjections:
 		features.TriggerIntrospectionProjections.set(level, event.Value)
-	case feature.KeyLegacyIntrospection:
-		features.LegacyIntrospection.set(level, event.Value)
 	case feature.KeyUserSchema:
 		features.UserSchema.set(level, event.Value)
 	case feature.KeyTokenExchange: