move tantivy-py installation to be separate from wheel (#97)

pypi does not allow packages to be uploaded that has a direct reference

for now we'll just ask the user to install tantivy separately

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Co-authored-by: Chang She <chang@lancedb.com>

python/tests/test_embeddings.py

@@ -14,7 +14,6 @@ import sys
 
 import numpy as np
 import pyarrow as pa
-
 from lancedb.embeddings import with_embeddings