Remove cf-encoding workaround

[aulemahal]

The encoding of cftime coordinates within sdba's map_blocks could be removed as the upstream issue in xarray seems to be fixed : pydata/xarray#5701. I don't know how it got fixed, but I believe the snippet below (and some other) and the xclim options can be safely removed. Or I guess the option should stay for 1 or 2 versions and emit a warning.

xclim/xclim/sdba/base.py

Lines 675 to 683 in 7acc410

	if OPTIONS[SDBA_ENCODE_CF]:
	ds = ds.copy()
	# Optimization to circumvent the slow pickle.dumps(cftime_array)
	# List of the keys to avoid changing the coords dict while iterating over it.
	for crd in list(ds.coords.keys()):
	if xr.core.common._contains_cftime_datetimes(
	ds[crd].variable
	): # noqa
	ds[crd] = xr.conventions.encode_cf_variable(ds[crd].variable)

FYI for xsdba, @coxipi