Revert "Add an error so unit tests fail."

This reverts commit 20aa7b0.

Author: drvinceknight

axelrod/tests/unit/test_match.py

@@ -21,7 +21,7 @@ def test_init(self, turns, game):
         self.assertEqual(match.result, [])
         self.assertEqual(match.players, [p1, p2])
         self.assertEqual(match.turns, turns)
-        self.assertEqual(match.prob_end, "foo")
+        self.assertEqual(match.prob_end, 0)
         self.assertEqual(match.noise, 0)
         self.assertEqual(match.game.RPST(), game.RPST())