Delete session *before* sending EndSession message

Typically we're sending an EndSession message because our session has
diverged from the remote party's session. So if we send an EndSession
message, but decrypt it with our old out-of-sync session, how can we
expect them to be able to decrypt it?

Instead, by deleting the existing sessions, we'll fetch a new PreKey,
and start fresh with the remote side.

// FREEBIE

Signal/src/Jobs/SessionResetJob.swift

@@ -25,12 +25,16 @@ class SessionResetJob: NSObject {
     func run() {
         Logger.info("\(TAG) Local user reset session.")
 
-        let endSessionMessage = EndSessionMessage(timestamp:NSDate.ows_millisecondTimeStamp(), in: thread)
+        OWSDispatch.sessionStoreQueue().async {
+            self.storageManager.deleteAllSessions(forContact: self.recipientId)
+
+            DispatchQueue.main.async {
+                let endSessionMessage = EndSessionMessage(timestamp:NSDate.ows_millisecondTimeStamp(), in: self.thread)
+
                 self.messageSender.send(endSessionMessage, success: {
                     Logger.info("\(self.TAG) successfully sent EndSession<essage.")
 
                     Logger.info("\(self.TAG) deleting sessions for recipient: \(self.recipientId)")
-            self.storageManager.deleteAllSessions(forContact: self.recipientId)
 
                     let message = TSInfoMessage(timestamp: NSDate.ows_millisecondTimeStamp(),
                                                 in: self.thread,
@@ -40,6 +44,8 @@ class SessionResetJob: NSObject {
                     Logger.error("\(self.TAG) failed to send EndSesionMessage with error: \(error.localizedDescription)")
                 })
             }
+        }
+    }
 
     class func run(contactThread: TSContactThread, messageSender: MessageSender, storageManager: TSStorageManager) {
         let job = self.init(recipientId: contactThread.contactIdentifier(),