How to remove duplicate songs from itunes playlist?

iTunes actually has a feature to display duplicates. It shows you all songs which it thinks are the same and you can delete one of them.

Here is a support page from Apple explaining how: Link

After selecting the playlist you would like remove duplicates from in iTunes, you'll then want to select "Name" in the "Sort By" menu (located under the "View" main menu item).

This will sort the songs in alphabetical order to where you can easily identify any duplicates since they'll appear right next to each other.

You'll then want to select a duplicated song and hover over the selected song to reveal the ... (More) menu.

Then select "Remove from Playlist" to delete the selected duplicated song.

And, just in case you're wondering, yes – doing this operation will only delete the selected duplicate, not all instances of the song within the playlist. (Which was a secret worry of mine.)