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 <[email protected]>

console/src/app/components/features/features.component.ts

@@ -33,7 +33,6 @@ const FEATURE_KEYS = [
   'enableBackChannelLogout',
   // 'improvedPerformance',
   'loginDefaultOrg',
-  'oidcLegacyIntrospection',
   'oidcSingleV1SessionTermination',
   'oidcTokenExchange',
   'oidcTriggerIntrospectionProjections',