Fix pep8 tests

We're now gating on pep8, so make it pass.  This removes a couple of
unused imports and fixes a typo in the CSV output code in the reviewers
command.

Change-Id: If77a18497b0efb48f59c10c0e4f5e8b3a8db5a7d

reviewstats/cmd/reviewers.py

@@ -113,7 +113,7 @@ def write_csv(reviewer_data, file_obj):
         )
     for (name, r_data, d_data, s_data) in reviewer_data:
         row = [name, r_data, d_data]
-        if ENABLED_RECEIVED:
+        if ENABLE_RECEIVED:
             row.append(s_data)
         writer.writerow(row)