investigation shows we don't use this timestamp for call error messages

SignalServiceKit/src/Messages/OWSOutgoingCallMessage.m

@@ -15,9 +15,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (instancetype)initWithThread:(TSThread *)thread
 {
-    // MJK TODO - investigate this.
+    // MJK TODO - safe to remove senderTimestamp
-    // These records aren't saved, but their timestamp is used in the event
-    // of a failing message send to insert the error at the appropriate place.
     self = [super initOutgoingMessageWithTimestamp:[NSDate ows_millisecondTimeStamp]
                                           inThread:thread
                                        messageBody:nil