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/query/user_grant.go

@@ -78,14 +78,6 @@ func NewUserGrantProjectIDSearchQuery(id string) (SearchQuery, error) {
 	return NewTextQuery(UserGrantProjectID, id, TextEquals)
 }
 
-func NewUserGrantProjectIDsSearchQuery(ids []string) (SearchQuery, error) {
-	list := make([]interface{}, len(ids))
-	for i, value := range ids {
-		list[i] = value
-	}
-	return NewListQuery(UserGrantProjectID, list, ListIn)
-}
-
 func NewUserGrantProjectOwnerSearchQuery(id string) (SearchQuery, error) {
 	return NewTextQuery(ProjectColumnResourceOwner, id, TextEquals)
 }