[lib][tests][clipboard] Remove nose

IPython/lib/tests/test_clipboard.py

@@ -1,5 +1,3 b''
-import nose.tools as nt
-
 from IPython.core.error import TryNext
 from IPython.lib.clipboard import ClipboardEmpty
 from IPython.testing.decorators import skip_if_no_x11
@@ -18,4 +16,4 b' def test_clipboard_get():'
         # No clipboard access API available
         pass
     else:
-        nt.assert_is_instance(a, str)
+        assert isinstance(a, str)