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/project_application_oidc.go

@@ -322,37 +322,6 @@ func (c *Commands) ChangeOIDCApplicationSecret(ctx context.Context, projectID, a
 	return result, err
 }
 
-func (c *Commands) VerifyOIDCClientSecret(ctx context.Context, projectID, appID, secret string) (err error) {
-	ctx, span := tracing.NewSpan(ctx)
-	defer func() { span.EndWithError(err) }()
-
-	app, err := c.getOIDCAppWriteModel(ctx, projectID, appID, "")
-	if err != nil {
-		return err
-	}
-	if !app.State.Exists() {
-		return zerrors.ThrowPreconditionFailed(nil, "COMMAND-D8hba", "Errors.Project.App.NotExisting")
-	}
-	if !app.IsOIDC() {
-		return zerrors.ThrowInvalidArgument(nil, "COMMAND-BHgn2", "Errors.Project.App.IsNotOIDC")
-	}
-	if app.HashedSecret == "" {
-		return zerrors.ThrowPreconditionFailed(nil, "COMMAND-D6hba", "Errors.Project.App.OIDCConfigInvalid")
-	}
-
-	projectAgg := ProjectAggregateFromWriteModel(&app.WriteModel)
-	ctx, spanPasswordComparison := tracing.NewNamedSpan(ctx, "passwap.Verify")
-	updated, err := c.secretHasher.Verify(app.HashedSecret, secret)
-	spanPasswordComparison.EndWithError(err)
-	if err != nil {
-		return zerrors.ThrowInvalidArgument(err, "COMMAND-Bz542", "Errors.Project.App.ClientSecretInvalid")
-	}
-	if updated != "" {
-		c.oidcUpdateSecret(ctx, projectAgg, appID, updated)
-	}
-	return nil
-}
-
 func (c *Commands) OIDCUpdateSecret(ctx context.Context, appID, projectID, resourceOwner, updated string) {
 	agg := project_repo.NewAggregate(projectID, resourceOwner)
 	c.oidcUpdateSecret(ctx, &agg.Aggregate, appID, updated)