Backport PR #2388 on branch 0.12.x (fix: remove zarr.convenience) (#2389)

Co-authored-by: Ilan Gold <ilanbassgold@gmail.com>

Author: meeseeksmachine

tests/test_readwrite.py

@@ -14,7 +14,6 @@
 import pandas as pd
 import pytest
 import zarr
-import zarr.convenience
 from scipy.sparse import csc_array, csc_matrix, csr_array, csr_matrix
 
 import anndata as ad