SCORM: Review convertAttemptToOffline function

In the convertAttemptToOffline function, we're calling scormOfflineProvider.getScormUserData to get the offline data. However, that function expects to receive a list of SCOs, and right now it isn't (this caused a bug that was temporarily fixed in MOBILE-2114).

This function also calculates some userdata, and maybe that isn't needed. Most of the calculated data is ignored, but using this function instead of just getting the stored data means that there are 3 fields that aren't stored in the DB when converting the attempt to offline: userid, scoid and timemodified. However, when creating a new offline attempt from scratch these values are stored to the offline DB. This is confusing.

We need to be really careful because any change in the stored data can have unexpected consequences.