[Telemetry] Resolve errors due to new pylint checker.

tools/telemetry/telemetry/util/exception_formatter.py

Index: tools/telemetry/telemetry/util/exception_formatter.py
diff --git a/tools/telemetry/telemetry/util/exception_formatter.py b/tools/telemetry/telemetry/util/exception_formatter.py
index 402461b5a2811f0c0f919884083af1aad5bb7170..8dd283168c45a3bac26271a0af6d81b538209e81 100644
--- a/tools/telemetry/telemetry/util/exception_formatter.py
+++ b/tools/telemetry/telemetry/util/exception_formatter.py
@@ -15,9 +15,8 @@ from telemetry.core import util
 
 def PrintFormattedException(exception_class=None, exception=None, tb=None,
                             msg=None):
-  if not (bool(exception_class) == bool(exception) == bool(tb)):
-    raise ValueError('Must specify all or none of '
-                     'exception_class, exception, and tb')
+  assert bool(exception_class) == bool(exception) == bool(tb), (
+      'Must specify all or none of exception_class, exception, and tb')
 
   if not exception_class:
     exception_class, exception, tb = sys.exc_info()