Remove unused imports and fix some other linter errors.

recipe_engine/unittests/recipe_test_api_test.py

 #!/usr/bin/env python
 # Copyright 2015 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
-import os
-import sys
 import unittest
 
 import test_env
 
 from recipe_engine import recipe_test_api
 
 class EXC(Exception):
   pass
 
 class TestExpectedException(unittest.TestCase):
@@ skipping 23 matching lines @@
 
   def testDisabledTestData(self):
     """Disabled test data correctly re-raises all exceptions."""
     test_data = recipe_test_api.TestData()
 
     with test_data.should_raise_exception(EXC()) as should_raise:
       self.assertTrue(should_raise)
 
 if __name__ == '__main__':
   unittest.main()