Remove deals from the index if they fail to seal on time or are slashed

SP reported seeing this error when retrieving:
ERROR retrieval impl/provider.go:379 Retrieval query: GetAsk: GetRetrievalPricingInput: failed to fetch storage deal state: 1 error occurred:
* deal 8835657 not found - deal may not have completed sealing before deal proposal start epoch, or deal may have been slashed

From Dirk:
The reason for the GetRetrievalPricingInput: failed to fetch error is because
the client attempts to retrieve deal 8835657
in order to work out the price of the deal, boost queries the chain for the deal's Piece Size and Verified Deal status
the deal is not on chain (presumably because it was not sealed in time)

TODO:
To fix this we should add code to boost that will remove deals from the index if they fail to seal on time or are slashed.