Remove stray nose import (#276)

Remove leftover nose import that does not seem to be used and causes
import failure when nose is not installed.

Author: mgorny

extra/test_hypothesis.py

@@ -6,7 +6,6 @@
 import sys
 import numbers
 
-from nose.plugins.skip import SkipTest
 from hypothesis import given, settings, assume, HealthCheck
 import hypothesis.strategies as st