docs: remove claim that sharding supports truncated boundary chunks

Author: d-v-b

changes/3802.feature.md

@@ -8,7 +8,6 @@ Rectilinear chunks can be used through:
   ``zarr.open``, and related functions, or to ``chunk_shape`` in ``zarr.create``.
 - **Opening existing arrays**: Arrays stored with the ``rectilinear`` chunk grid are read
   transparently via ``zarr.open`` and ``zarr.open_array``.
-- **Rectilinear sharding**: Shard boundaries can be rectilinear while inner chunks remain regular.
 
 **Breaking change**: The ``validate`` method on ``BaseCodec`` and ``CodecPipeline`` now receives
 a ``ChunkGridMetadata`` instance instead of a ``ChunkGrid`` instance for the ``chunk_grid``