In among the MC provided Smartlists you should find one called "Audio -- Task -- Possible duplicates" that will provide you with a list of every track that has a duplicate. The list will contain 2 entries for each Duplicated Track.Make a note of the what is in the box alongside "Modify Results" Rule "Only Duplicates" entry then set up anther Smartlist using the "Audio -- Task -- Possible duplicates" Smartist as the input and set up a "Modify Results" Rule selecting "Remove duplicates of" from the dropdown and list and put the same value in the 2nd box to the one that is in the "Audio -- Task -- Possible duplicates" Smartlist.When you run it you should get a list containing 1 copy of the Duplicated Tracks, check to make sure the total number of files is 50% of the number of tracks from the first list.Once you are certain the list only contains 1 entry for each duplicated track select all the tracks and delete them.
They're probably in different locations. So sorting by location. Or search for the location you want to remove, then delete.