Exceptions: Failure, UntrustedIdentity
+sendViewedReceipt(recipient<s>, targetSentTimestamp<ax>) -> <>::
+* recipient : Phone number of a single recipient
+* targetSentTimestamp : Array of Longs to identify the corresponding signal messages
+
+Exceptions: Failure, UntrustedIdentity
+
sendRemoteDeleteMessage(targetSentTimestamp<x>, recipient<s>) -> timestamp<x>::
sendRemoteDeleteMessage(targetSentTimestamp<x>, recipients<as>) -> timestamp<x>::
* targetSentTimestamp : Long representing timestamp of the message to delete