Reader Xls Dead Code (#3756)

* Reader Xls Dead Code

Recent changes left Xls Reader with a ton of Scrutinizer messages. I have filtered away the false positives. Most of what is left is dead code, and this PR addresses those. Most of those are used to parse the BIFF data, but we either don't need to implement, or haven't yet implemented, those particular parsed data items. I think it is more useful to comment those out for documetary purposes rather than deleting them.

* Missed a Few