Revert changes in worker.GunicornWebWorker

Reverts changes in `worker.GunicornWebWorker` according to
#1 (comment)

They could be introduced in a separate PR.

aiohttp/worker.py

@@ -34,9 +34,7 @@ def run(self):
         self._runner = ensure_future(self._run(), loop=self.loop)
 
         try:
-            self.loop.run_until_complete(asyncio.gather(self._runner,
-                                                        self.wsgi.startup(),
-                                                        loop=self.loop))
+            self.loop.run_until_complete(self._runner)
         finally:
             self.loop.close()