remove non-existent chunks method from API docs page

Author: TomNicholas

docs/source/api.rst

@@ -57,7 +57,6 @@ This interface echoes that of ``xarray.Dataset``.
    DataTree.attrs
    DataTree.encoding
    DataTree.indexes
-   DataTree.chunks
    DataTree.nbytes
    DataTree.ds
    DataTree.to_dataset
@@ -66,11 +65,6 @@ This interface echoes that of ``xarray.Dataset``.
    DataTree.is_empty
    DataTree.is_hollow
 
-..
-
-   Missing:
-   ``DataTree.chunksizes``
-
 Dictionary interface
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