Removing duplicate code block that raises exception (#16568)

For TensorFlow version 1.5.0-rc1, the code block below raises a `ValueError`. Simply remove the duplication (lines 274 - 277 are exactly the same) and the issue is resolved.

```
# Add returned summaries to writer in each step.
writer.add_summary(summary, step)
# Add metadata to visualize the graph for the last run.
if step == (num_steps - 1):
      writer.add_run_metadata(run_metadata, 'step%d' % step)
```