kiji-express-music: EXP-330. Remove Kiji Modeling references from Express Music tutorial

issue: https://jira.kiji.org/browse/EXP-330
review: https://review.kiji.org/r/1415
commit: https://github.com/kijiproject/kiji-express-music/commit/bed19e793e66060691b506fef4320d783ee7b1f7