remove xarray monkey patches in connectivity generation script

[chrisbarber]

At some point it should be possible to remove

datacube/scripts/datasets/connectivity.py

Lines 616 to 625 in af79f76

	# monkey patch to get zarr to ignore dask chunks and use its own heuristics
	def copy_func(f):
	g = types.FunctionType(f.__code__, f.__globals__, name=f.__name__,
	argdefs=f.__defaults__,
	closure=f.__closure__)
	g = functools.update_wrapper(g, f)
	g.__kwdefaults__ = f.__kwdefaults__
	return g
	orig_determine_zarr_chunks = copy_func(xr.backends.zarr._determine_zarr_chunks)
	xr.backends.zarr._determine_zarr_chunks = lambda enc_chunks, var_chunks, ndim: orig_determine_zarr_chunks(enc_chunks, None, ndim)

and

datacube/scripts/datasets/connectivity.py

Lines 632 to 645 in af79f76

	# monkey patch to make dask arrays writable with different chunks than zarr dest
	# could do without this but would have to contend with 'inconsistent chunks' on dataset
	def sync_using_zarr_copy(self, compute=True):
	if self.sources:
	import dask.array as da
	rechunked_sources = [source.rechunk(target.chunks)
	for source, target in zip(self.sources, self.targets)]
	delayed_store = da.store(rechunked_sources, self.targets,
	lock=self.lock, compute=compute,
	flush=True)
	self.sources = []
	self.targets = []
	return delayed_store
	xr.backends.common.ArrayWriter.sync = sync_using_zarr_copy

'chunks': None here may need to be removed at the same time.

Xarray 0.10.8 has made some improvement in fixing this, but there are still some issues (see pydata/xarray#2300). This needs to be carefully tested for performance since some chunk configurations can cause a large amount of data to be loaded into memory during certain queries. This might be another bug; more investigation is needed.