Add DeleteMessage to dmReceiver, make web worker connection for DeleteMessage in dm indexedDb, and fix dmReceiver

Add test case explicit to what was happening in the manual testing for the duplicate upsertMessage issue

Do not error out when this message already exists inside the DB. Instead, set the ID and re-attempt as an upsert.

Make it clear we are working with a partnerToken and fix bug where we updated a conversation to the senderKey and not the partnerKey