Dictionary(uniqueKeysWithValues:) will assert that the provided keys are
unique and crash if a violation occurs. The existing code in
OWSReceiptManager falsely assumes that the addresses being built are
unique.
The keys in the key value store *are* unique, but as they're mapped into
addresses, we may have learned of a high trust e164/UUID mapping since
they were inserted. As the identifiers are mapped into
SignalServiceAddresses, the e164 and UUID are mapped to the same
SignalServiceAddress.
The fix is to just wrap our address builder in a Set() so we only have
one copy for each address.
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