From this IndiaFM piece:
Director Imtiaz Ali reluctantly admits the song was pulled off. "It went perfectly with Kareena's character and the film’s mood. In fact I didn't only want to use it in the first promo but all the promotional campaigns and also as part of the background music in my film."
Rather than risk a sticky copyright-infringement situation, Imtiaz decided to pull the plug on the track. This latest incident of copyright consciousness in Bollywood is part of a larger campaign to acknowledge and legitimize all derived works in Hindi cinema...
Here is the trailer in question: