torch: remove unused sparse_row function

Author: mdekstrand

src/lenskit/torch.py

@@ -27,25 +27,6 @@ def wrapper(*args, **kwargs):
     return wrapper
 
 
-def sparse_row(mat: torch.Tensor, row: int) -> torch.Tensor:
-    """
-    Get a row of a sparse (CSR) tensor.  This is needed because indexing a
-    tensor does not work in inference mode.
-    """
-
-    assert mat.is_sparse_csr
-
-    cri = mat.crow_indices()
-    sp = cri[row]
-    ep = cri[row + 1]
-
-    cs = mat.col_indices()
-    vs = mat.values()
-    return torch.sparse_coo_tensor(
-        indices=cs[sp:ep].reshape(1, -1), values=vs[sp:ep], size=mat.shape[1:]
-    )
-
-
 def safe_tensor(array) -> torch.Tensor:
     """
     Safely convert an array into a NumPy tensor.  This includes copying it to