Retry stage must log error if entries cannot be removed from retry registry

[akara]

In cases where the context instance changes in the stages to be retried and there is no identity provider, the hash code is used as the identity. As this context changes, the removal of the entry from the retry registry will fail or not match, quietly. This becomes a memory leak.

While we cannot change the API, such mismatches need to be identified and logged as "Error".

[sebady]

fixed