Deserializing arrays should not trigger load_metadata

[rabernat]

Currently the __setstate__ method on Array just calls __init__.

zarr-python/zarr/core.py

Lines 2567 to 2568 in 6105ef2

	def __setstate__(self, state):
	self.__init__(**state)

And __init__ contains a call to load_metadata

zarr-python/zarr/core.py

Lines 169 to 170 in 6105ef2

	# initialize metadata
	self._load_metadata()

This really doesn't make much sense. We should serialize the metadata up with the array.