Removed extra doSessionInit call

* This extra doSessionInit if we init a 2nd time isn't needed and
address the issue covered in the new initWithContext_calledA2ndTimeAfter30OrMoreSeconds_doesNotStartNewSession test added in this PR.
* For reference the extra doSessionInit call was added in this commit
* 012cdb2#diff-2708f86f77e539cab647ecede9d5fcbead3bf0f954d7f9e536eafbc78ba760d6R685
* Ran `shouldSendTagsFromBackgroundOnAppKilled` test locally and it still passes after this change

Author: jkasten2

OneSignalSDK/onesignal/src/main/java/com/onesignal/OneSignal.java

@@ -692,7 +692,6 @@ synchronized private static void init(Context context) {
          if (notificationOpenedHandler != null)
             fireCallbackForOpenedNotifications();
          logger.debug("OneSignal SDK initialization already completed.");
-         doSessionInit();
          return;
       }