Remove another future import.

src/allmydata/test/storage_plugin.py

@@ -5,7 +5,6 @@
 Ported to Python 3.
 """
 
-from future.utils import native_str_to_bytes
 from six import ensure_str
 
 import attr
@@ -87,7 +86,7 @@ def get_client_resource(self, configuration):
         """
         items = configuration.items(self._client_section_name, [])
         resource = Data(
-            native_str_to_bytes(dumps(dict(items))),
+            dumps(dict(items)).encode("utf-8"),
             ensure_str("text/json"),
         )
         # Give it some dynamic stuff too.
@@ -105,7 +104,7 @@ class GetCounter(Resource, object):
     value = 0
     def render_GET(self, request):
         self.value += 1
-        return native_str_to_bytes(dumps({"value": self.value}))
+        return dumps({"value": self.value}).encode("utf-8")
 
 
 @implementer(RIDummy)