Remove downloads or remove from library for duplicate playlist?
Remove Downloads will leave the playlist in your library, but remove the music files associated with the songs in that playlist from your phone, thus freeing up storage. It's a quick method to bulk-remove songs from your phone.

Delete from Library will remove the playlist itself from your media library (including iCloud Music Library if you use iTunes Match or MUSIC). However whatever music files you've already downloaded will remain on your phone.

In your case, you should Delete from Library if you are certain the playlist is a duplicate.