This API complements module subscribe by enabling modules to unsubscribe
from specific keyspace event notifications when they are no longer
needed.
This helps reduce performance overhead and unnecessary callback
invocations.
The function matches subscriptions based on event mask, callback
pointer,
and module identity. If a matching subscription is found, it is removed.
Returns REDISMODULE_OK if a subscription was successfully removed,
otherwise REDISMODULE_ERR.
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