remove redundant exception handling an async base

StopIteration is simply propogated, so there's no reason to catch it.
The catch-all exception is also caught and logged in handle(), but
broken pipe errors are ignored. The redundant catch here was generating
excess logging by calling handle_error for a broken pipe which fails to
send the error because the client has already disconnected.

gunicorn/workers/async.py

@@ -71,12 +71,6 @@ class AsyncWorker(base.Worker):
                   respiter.close()
             if resp.should_close():
                 raise StopIteration()
-        except StopIteration:
-            raise
-        except Exception, e:
-            #Only send back traceback in HTTP in debug mode.
-            self.handle_error(sock, e)
-            return False
         finally:
             try:
                 self.cfg.post_request(self, req)