Shadow Maps are "painted" shadows on terrain which don't disappear when models are hidden/deleted/moved. This is an issue with Blizzard's maps, especially Vanilla ones. I can't imagine anyone actually using Shadow Maps, but tool for editing them still could be nice to have.
For now, it would be more than useful to have at least enable/disable shadow maps on chunk/ADT. I went through whole MCNKs struct in 010, and I have edited in header of each mcnk in each row flags, removing flag 1. That did the job, and I didn't have any issues with using this method yet.
For those interrested in getting rid of static shadows on Blizzlike maps for purpouses of editing them, I have released my 010 script on my YT channel and in my toolpack.
@Amaroth suggests:
which often comes up as well.