Hnmm, sorry to say but, that is a mess, even if there was a command for remove duplicates it would not make much difference, as in some places you have 3 arcs on top of a lot of lines, (the lines were probably arcs which had got exploded twice). and in other places there are multiple lines on top of polylines. There is no way I know of making the restoration job simple. You can turn off preferences - selection - use choices, then create a new layer, select one of every line or arc and put on the new layer, then once completed, get rid everything except this new layer. or use the method I posted above on every line and arc, ## Edit ## or use Johns method which was posted while I was typing. ## End Edit ##. either way its going to be a pain.
I do not think this was caused by using make copy, nor forgetting to turn it off, Going off your other drawing where you subsequently used select all - place on workplane, did you do that with this drawing. I ask, because in your other drawing you have duplicates on different z locations, which, if you did not check for duplicates first, when using select all - place on workplane, would cause duplicate lines in the same place, the exploded arcs may have been accidental, or as a result of multiple DWG save (just a guess).
If it was me, I'd copy what was required from your previous drawing (before things were put on workplane), Or if not possible. I'd just bite the bullet and trace over the drawing using polylines / arcs, using a different pen colour on a new layer. then once re-drawn delete everything except the new layer stuff.