How to remove shadows cast by Structures?

It would be pretty difficult to do so, but adding glowstone or torches underneath carpets will remove the large shadow. I would recommend using green carpets, to blend with the grass. If you want, you could also use daylight sensors to turn on and off Redstone lamps for when it turns to nighttime so that the light doesn't look too out of place.

If you want to make it mob spawn proof, then I suggest the answer given by @Banana97286 i.e. use glowstone/sea lanterns, and cover with carpets. If you want to change just how it looks for you, use a fullbright resourcepack.