"Due to music licensing restrictions, we are required to remove certain songs from the in-game soundtrack of Grand Theft Auto IV and its Episodes, in particular a large portion of the Russian pop station, Vladivostok FM," a Rockstar representative said. "However, we are replacing some of those songs with a new set of songs on that station. We will update our customer support website with new information as soon as it is available."
The upcoming loss is disappointing, but not entirely surprising. It is unknown when the music will be removed, but an article from Kotaku UK, who confirmed the news in this article, report that it is likely to be removed on April 26th.