InMemory deduplication storage doesn't clean old entries

[andreasohlund]

Eventually causing the endpoint to run out of memory.

See Particular/NServiceBus#3564 for more details

[ramonsmits]

@andreasohlund Why is the issue closed in NServiceBus? The inmemory persister is part of core.

[andreasohlund]

Figured this was the better place but have no strong opinion