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/scripts/pipeline_generator.py

@@ -3,7 +3,6 @@
 import os
 import sys
 import argparse
-import itertools
 import json
 import textwrap
 
@@ -31,7 +30,7 @@ disabled_passes = sum(args.disable_pass, [])
 disabled_passpipelines = sum(args.disable_passpipeline, [])
 
 # First filter out pipelines.
-normal_pipeline_generated = [x.generate() for x in normal_pipeline if not x.identifier in disabled_passpipelines]
+normal_pipeline_generated = [x.generate() for x in normal_pipeline if x.identifier not in disabled_passpipelines]
 
 # Then filter out specific passes.
 for i in range(len(normal_pipeline_generated)):

utils/pass-pipeline/scripts/pipelines_build_script.py

@@ -9,7 +9,6 @@ import textwrap
 # Append the src dir
 sys.path.append(os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), 'src'))
 
-import pass_pipeline_library
 import passes
 
 # TODO: This should not be hard coded.