Normalize all source encoding declarations

testing/code/test_excinfo.py

@@ -1,4 +1,4 @@
-# -*- coding: utf-8 -*-
+# coding: utf-8
 from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function

testing/code/test_source.py

@@ -1,4 +1,4 @@
-# -*- coding: utf-8 -*-
+# coding: utf-8
 # flake8: noqa
 # disable flake check on this file because some constructs are strange
 # or redundant on purpose and can't be disable on a line-by-line basis