Drop decode from ConsolidatedMetadataStore (#452)

This call to `decode` has been made unnecessary thanks to the
`json_loads` utility function used here. Unfortunately this code was
left over when that was added in. Drop this now unneeded code so as to
better handle `bytes`-like data.

Author: jakirkham

zarr/storage.py

@@ -2451,11 +2451,7 @@ def __init__(self, store, metadata_key='.zmetadata'):
         self.store = store
 
         # retrieve consolidated metadata
-        if sys.version_info.major == 3 and sys.version_info.minor < 6:
-            d = store[metadata_key].decode()  # pragma: no cover
-        else:  # pragma: no cover
-            d = store[metadata_key]
-        meta = json_loads(d)
+        meta = json_loads(store[metadata_key])
 
         # check format of consolidated metadata
         consolidated_format = meta.get('zarr_consolidated_format', None)