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>

console/src/assets/i18n/en.json

@@ -1627,8 +1627,6 @@
     "FEATURES": {
       "LOGINDEFAULTORG": "Login Default Org",
       "LOGINDEFAULTORG_DESCRIPTION": "The login UI will use the settings of the default org (and not from the instance) if no organization context is set",
-      "OIDCLEGACYINTROSPECTION": "OIDC Legacy introspection",
-      "OIDCLEGACYINTROSPECTION_DESCRIPTION": "We have recently refactored the introspection endpoint for performance reasons. This feature can be used to rollback to the legacy implementation if unexpected bugs arise.",
       "OIDCTOKENEXCHANGE": "OIDC Token Exchange",
       "OIDCTOKENEXCHANGE_DESCRIPTION": "Enable the experimental urn:ietf:params:oauth:grant-type:token-exchange grant type for the OIDC token endpoint. Token exchange can be used to request tokens with a lesser scope or impersonate other users. See the security policy to allow impersonation on an instance.",
       "OIDCTRIGGERINTROSPECTIONPROJECTIONS": "OIDC Trigger introspection Projections",