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/authn_key_test.go

@@ -423,55 +423,6 @@ func Test_AuthNKeyPrepares(t *testing.T) {
 			},
 			object: (*AuthNKey)(nil),
 		},
-		{
-			name:    "prepareAuthNKeyPublicKeyQuery no result",
-			prepare: prepareAuthNKeyPublicKeyQuery,
-			want: want{
-				sqlExpectations: mockQueriesScanErr(
-					regexp.QuoteMeta(prepareAuthNKeyPublicKeyStmt),
-					nil,
-					nil,
-				),
-				err: func(err error) (error, bool) {
-					if !zerrors.IsNotFound(err) {
-						return fmt.Errorf("err should be zitadel.NotFoundError got: %w", err), false
-					}
-					return nil, true
-				},
-			},
-			object: ([]byte)(nil),
-		},
-		{
-			name:    "prepareAuthNKeyPublicKeyQuery found",
-			prepare: prepareAuthNKeyPublicKeyQuery,
-			want: want{
-				sqlExpectations: mockQuery(
-					regexp.QuoteMeta(prepareAuthNKeyPublicKeyStmt),
-					prepareAuthNKeyPublicKeyCols,
-					[]driver.Value{
-						[]byte("publicKey"),
-					},
-				),
-			},
-			object: []byte("publicKey"),
-		},
-		{
-			name:    "prepareAuthNKeyPublicKeyQuery sql err",
-			prepare: prepareAuthNKeyPublicKeyQuery,
-			want: want{
-				sqlExpectations: mockQueryErr(
-					regexp.QuoteMeta(prepareAuthNKeyPublicKeyStmt),
-					sql.ErrConnDone,
-				),
-				err: func(err error) (error, bool) {
-					if !errors.Is(err, sql.ErrConnDone) {
-						return fmt.Errorf("err should be sql.ErrConnDone got: %w", err), false
-					}
-					return nil, true
-				},
-			},
-			object: ([]byte)(nil),
-		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {