No longer warn and convert ndarray subclasses

[braingram]

Description of the problem

With asdf 4.0 we can drop supporting unknown ndarray subclasses:

asdf/asdf/config.py

Line 28 in f3f6070

DEFAULT_CONVERT_UNKNOWN_NDARRAY_SUBCLASSES = True

asdf/asdf/yamlutil.py

Lines 304 to 310 in f3f6070

	if convert_ndarray_subclasses and isinstance(obj, np.ndarray):
	warnings.warn(
	f"A ndarray subclass ({type(obj)}) was converted as a ndarray. "
	"This behavior will be removed from a future version of ASDF. "
	"See https://asdf.readthedocs.io/en/latest/asdf/config.html#convert-unknown-ndarray-subclasses",
	AsdfConversionWarning,
	)