Rename 'throwaway' variables to single underscore

Also removed unused ones

whipper/command/main.py

@@ -52,7 +52,7 @@ def main():
         return 1
     except KeyboardInterrupt:
         return 2
-    except ImportError as e:
+    except ImportError:
         raise
     except task.TaskException as e:
         if isinstance(e.exception, ImportError):

whipper/command/offset.py

@@ -88,7 +88,6 @@ CD in the AccurateRip database."""
         table = t.table
 
         logger.debug("CDDB disc id: %r", table.getCDDBDiscId())
-        responses = None
         try:
             responses = accurip.get_db_entry(table.accuraterip_path())
         except accurip.EntryNotFound: