Remove Album Art from Lock Screen
I guess the music application you are using (probably Apollo in your case) is responsible for this. You might want to try a different one.

I just dug into Apollos source code and think I have found where it sets the album artwork. Check out line 1377 on Github.

mRemoteControlClient.putBitmap(RemoteControlClient.MetadataEditor.BITMAP_KEY_ARTWORK, albumArt);
  

The way I see it, the call to RemoteControlClient is responsible for setting the album art and other things. So, the media player is responsible for your problem and unlike you find one that doesn't provide the album art to the RemoteControlClient you probably can't do much about it.