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/command/system_features_test.go

@@ -81,24 +81,6 @@ func TestCommands_SetSystemFeatures(t *testing.T) {
 				ResourceOwner: "SYSTEM",
 			},
 		},
-		{
-			name: "set LegacyIntrospection",
-			eventstore: expectEventstore(
-				expectFilter(),
-				expectPush(
-					feature_v2.NewSetEvent[bool](
-						context.Background(), aggregate,
-						feature_v2.SystemLegacyIntrospectionEventType, true,
-					),
-				),
-			),
-			args: args{context.Background(), &SystemFeatures{
-				LegacyIntrospection: gu.Ptr(true),
-			}},
-			want: &domain.ObjectDetails{
-				ResourceOwner: "SYSTEM",
-			},
-		},
 		{
 			name: "set UserSchema",
 			eventstore: expectEventstore(
@@ -124,12 +106,12 @@ func TestCommands_SetSystemFeatures(t *testing.T) {
 				expectPushFailed(io.ErrClosedPipe,
 					feature_v2.NewSetEvent[bool](
 						context.Background(), aggregate,
-						feature_v2.SystemLegacyIntrospectionEventType, true,
+						feature_v2.SystemEnableBackChannelLogout, true,
 					),
 				),
 			),
 			args: args{context.Background(), &SystemFeatures{
-				LegacyIntrospection: gu.Ptr(true),
+				EnableBackChannelLogout: gu.Ptr(true),
 			}},
 			wantErr: io.ErrClosedPipe,
 		},
@@ -146,10 +128,6 @@ func TestCommands_SetSystemFeatures(t *testing.T) {
 						context.Background(), aggregate,
 						feature_v2.SystemTriggerIntrospectionProjectionsEventType, false,
 					),
-					feature_v2.NewSetEvent[bool](
-						context.Background(), aggregate,
-						feature_v2.SystemLegacyIntrospectionEventType, true,
-					),
 					feature_v2.NewSetEvent[bool](
 						context.Background(), aggregate,
 						feature_v2.SystemUserSchemaEventType, true,
@@ -163,7 +141,6 @@ func TestCommands_SetSystemFeatures(t *testing.T) {
 			args: args{context.Background(), &SystemFeatures{
 				LoginDefaultOrg:                 gu.Ptr(true),
 				TriggerIntrospectionProjections: gu.Ptr(false),
-				LegacyIntrospection:             gu.Ptr(true),
 				UserSchema:                      gu.Ptr(true),
 				OIDCSingleV1SessionTermination:  gu.Ptr(true),
 			}},
@@ -192,10 +169,6 @@ func TestCommands_SetSystemFeatures(t *testing.T) {
 						context.Background(), aggregate,
 						feature_v2.SystemLoginDefaultOrgEventType, false,
 					)),
-					eventFromEventPusher(feature_v2.NewSetEvent[bool](
-						context.Background(), aggregate,
-						feature_v2.SystemLegacyIntrospectionEventType, true,
-					)),
 				),
 				expectPush(
 					feature_v2.NewSetEvent[bool](
@@ -219,7 +192,6 @@ func TestCommands_SetSystemFeatures(t *testing.T) {
 			args: args{context.Background(), &SystemFeatures{
 				LoginDefaultOrg:                 gu.Ptr(true),
 				TriggerIntrospectionProjections: gu.Ptr(false),
-				LegacyIntrospection:             gu.Ptr(true),
 				UserSchema:                      gu.Ptr(true),
 				OIDCSingleV1SessionTermination:  gu.Ptr(false),
 			}},