Removes dead code.

rob-smallshire · rob-smallshire · commit 0457ca989056 · 2017-01-22T13:55:23.000+01:00
diff --git a/serial_asyncio/__init__.py b/serial_asyncio/__init__.py
@@ -240,7 +240,6 @@ def _write_ready(self):
         argument.
         """
         data = b''.join(self._write_buffer)
-        num_bytes = len(data)
         assert data, 'Write buffer should not be empty'
 
         self._write_buffer.clear()
