Remove enriched content before storing events to `AggregateStorage`

[armiol]

Similar to #581, a storage of Aggregate event records also stores event enrichments, that aren't needed and take a lot of space.

This always happen in case an instance of Aggregate reacts upon an enriched Event and emits own events in response. Each of the emitted events references an original event context, which contains enrichments.

This should be addressed in a way, so that enrichments are removed before storing the event records for a particular Aggregate type.

[dmytro-grankin]

Resolved in #602.