Various Python cleanups

Fixes:
* Unused import
* Redundant backslash
* Use of discouraged if not x in y
* Use of deprecated form of raising exceptions

Follow-up to PR #655 as requested by @gribozavr

utils/pass-pipeline/src/pass_pipeline.py

@@ -1,8 +1,3 @@
-
-import sys
-import json
-import itertools
-
 class Pass(object):
     def __init__(self, name):
         self.name = name