Remove unused import fallback on the 'mock' library

test/test_yn.py

@@ -30,17 +30,10 @@
 
 import sys
 import unittest
+from unittest import mock
 from supybot import questions
 from supybot.test import SupyTestCase
 
-try:
-    from unittest import mock  # Python 3.3+
-except ImportError:
-    try:
-        import mock  # Everything else, an external 'mock' library
-    except ImportError:
-        mock = None
-
 # so complicated construction because I want to
 # gain the string 'y' instead of the character 'y'
 # the reason of usage this construction is to prove