Remove unused org-music as an indexable content type from Khoj

Org-music was just a custom content type that worked with org-music.
It was mostly only useful for me.

Cleaning up that code will reduce number of content types for khoj to
manage.

docker-compose.yml

@@ -19,7 +19,6 @@ services:
       - ./tests/data/org/:/data/org/
       - ./tests/data/images/:/data/images/
       - ./tests/data/ledger/:/data/ledger/
-      - ./tests/data/music/:/data/music/
       - ./tests/data/markdown/:/data/markdown/
       - ./tests/data/pdf/:/data/pdf/
       # Embeddings and models are populated after the first run