remove no longer used dojo/_base/unload dependency, refs #15206
remove no longer used  dojo/_base/unload and dojo/_base/win dependencies, refs #12799 !strict
remove use of deprecated dojo/_base/unload::addOnWindowUnload, refs #16585 !strict
fix old comments that refer to dojo/_base/window::doc, even though it isn't being used anymore, refs #15216 !strict