CBG-2206: TestReplicatorDoNotSendDeltaWhenSrcIsTombstone flake

[gregns1]

CBG-2206

• Test was asserting on 404 missing on fetching the specific rev via rest api. This is incorrect as you will still get 200 code but with _deleted body. Changed test to reflect this + had a check that fetching the doc (and not specifying rev id returned 404)
• In addition I noticed that on destination when the delete delta was being replicated over, we were patching the empty delta to the revision on the destination. Meaning we would have _deleted in the body but also the old body fields too. The example from the test looked like so:

{"_deleted":true,"_id":"test","_rev":"2-26ddda6a2110ff1a408ebb8d36674b17","field1":"f1_1","field2":"f2_1"}

• To fix I added statement to only patch if the incoming delta is not a delete.

Pre-review checklist

• Removed debug logging (fmt.Print, log.Print, ...)
• Logging sensitive data? Make sure it's tagged (e.g. base.UD(docID), base.MD(dbName))
• Updated relevant information in the API specifications (such as endpoint descriptions, schemas, ...) in docs/api

Integration Tests

• GSI=true,xattrs=true https://jenkins.sgwdev.com/job/SyncGateway-Integration/2562/

[adamcfraser]

We don't intend to support deltas for deletes (i.e. if deleted and deltaSrc properties are both specified on an incoming rev message, we should ignore deltaSrc, and perform this check up on line 1016).