removed frame_list variable from load_tag to get rid of -Wunused-variabl...

Hello!
I have decided to use your id3 lib for a c program I am working on which will (hopefully) remove duplicate audio files from a large music collection.
This pull request removes the frame_list variable from load_tag. I added the gcc flag -Wall, which generated a warning about this variable.
Looking forward to playing with your id3 implementation.