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/api/grpc/feature/v2beta/converter_test.go

@@ -20,7 +20,6 @@ func Test_systemFeaturesToCommand(t *testing.T) {
 	arg := &feature_pb.SetSystemFeaturesRequest{
 		LoginDefaultOrg:                     gu.Ptr(true),
 		OidcTriggerIntrospectionProjections: gu.Ptr(false),
-		OidcLegacyIntrospection:             nil,
 		UserSchema:                          gu.Ptr(true),
 		OidcTokenExchange:                   gu.Ptr(true),
 		ImprovedPerformance:                 nil,
@@ -29,7 +28,6 @@ func Test_systemFeaturesToCommand(t *testing.T) {
 	want := &command.SystemFeatures{
 		LoginDefaultOrg:                 gu.Ptr(true),
 		TriggerIntrospectionProjections: gu.Ptr(false),
-		LegacyIntrospection:             nil,
 		UserSchema:                      gu.Ptr(true),
 		TokenExchange:                   gu.Ptr(true),
 		ImprovedPerformance:             nil,
@@ -54,10 +52,6 @@ func Test_systemFeaturesToPb(t *testing.T) {
 			Level: feature.LevelUnspecified,
 			Value: false,
 		},
-		LegacyIntrospection: query.FeatureSource[bool]{
-			Level: feature.LevelSystem,
-			Value: true,
-		},
 		UserSchema: query.FeatureSource[bool]{
 			Level: feature.LevelSystem,
 			Value: true,
@@ -89,10 +83,6 @@ func Test_systemFeaturesToPb(t *testing.T) {
 			Enabled: false,
 			Source:  feature_pb.Source_SOURCE_UNSPECIFIED,
 		},
-		OidcLegacyIntrospection: &feature_pb.FeatureFlag{
-			Enabled: true,
-			Source:  feature_pb.Source_SOURCE_SYSTEM,
-		},
 		UserSchema: &feature_pb.FeatureFlag{
 			Enabled: true,
 			Source:  feature_pb.Source_SOURCE_SYSTEM,
@@ -118,7 +108,6 @@ func Test_instanceFeaturesToCommand(t *testing.T) {
 	arg := &feature_pb.SetInstanceFeaturesRequest{
 		LoginDefaultOrg:                     gu.Ptr(true),
 		OidcTriggerIntrospectionProjections: gu.Ptr(false),
-		OidcLegacyIntrospection:             nil,
 		UserSchema:                          gu.Ptr(true),
 		OidcTokenExchange:                   gu.Ptr(true),
 		ImprovedPerformance:                 nil,
@@ -128,7 +117,6 @@ func Test_instanceFeaturesToCommand(t *testing.T) {
 	want := &command.InstanceFeatures{
 		LoginDefaultOrg:                 gu.Ptr(true),
 		TriggerIntrospectionProjections: gu.Ptr(false),
-		LegacyIntrospection:             nil,
 		UserSchema:                      gu.Ptr(true),
 		TokenExchange:                   gu.Ptr(true),
 		ImprovedPerformance:             nil,
@@ -154,10 +142,6 @@ func Test_instanceFeaturesToPb(t *testing.T) {
 			Level: feature.LevelUnspecified,
 			Value: false,
 		},
-		LegacyIntrospection: query.FeatureSource[bool]{
-			Level: feature.LevelInstance,
-			Value: true,
-		},
 		UserSchema: query.FeatureSource[bool]{
 			Level: feature.LevelInstance,
 			Value: true,
@@ -193,10 +177,6 @@ func Test_instanceFeaturesToPb(t *testing.T) {
 			Enabled: false,
 			Source:  feature_pb.Source_SOURCE_UNSPECIFIED,
 		},
-		OidcLegacyIntrospection: &feature_pb.FeatureFlag{
-			Enabled: true,
-			Source:  feature_pb.Source_SOURCE_INSTANCE,
-		},
 		UserSchema: &feature_pb.FeatureFlag{
 			Enabled: true,
 			Source:  feature_pb.Source_SOURCE_INSTANCE,