Remove no longer needed IE 11 workarounds

As of IE 11.0.12 (KB2977629), many of the workarounds we have in place for IE 11 are no longer needed.  I tested this by removing all of the `isInternetExplorer` checks sprinkled throughout the code and then putting back the ones that were still needed (i.e. failing tests).  Then I ran through the Sandcastle examples just to be sure.

@pjcozzi or @kring should probably review this, since they did a lot of the initial work to get things happy in IE.