Remove unnecessary ACCESS_TO_REFRESH tuple in RedisTokenStore

[Mert-Z]

Tuples stored with ACCESS_TO_REFRESH key are never queried. Can it be removed or is it left intentionally for future use? If for future use, can it be documented via code comments?

If we remove its references, we can also get rid of the bug on L313 where ACCESS_TO_REFRESH is tried to be cleared by serializing with refresh token as key whereas it should be cleared by serializing related access token as key.