Those items in the picture can be removed, but not the mission items, like old poems, keys, books, etc, or even trophies (I think I can sell them but I don't want to), the thing is that, also, the weight doesn't change either
Yes I used a trainer before, my inventory is full of mission's items.
I did a clean installation, but when i restore my save game the inventory is still the same.
I haven't see corrupted item descriptions, but there is lag and slowdown when opening or closing