Fix remove_specific_occurrences function

user_playlist_remove_specific_occurrences_of_tracks is expecting a
different tracklist object to the one that is documented, causing a
"'dict' object has no attribute 'split'" error. Update it to expect the
correct format.
Merge pull request #36 from mattduck/fix-fn-remove-specific-occurrences

Fix remove_specific_occurrences function