pylint: fix KeyError: <type 'numpy.ufunc'> visible with pandas 0.24.2

Updating pandas to 0.24.2 revealed as :

      File "develop-eggs/astroid-1.3.8+slapospatched001-py2.7.egg/astroid/raw_building.py", line 360, in _set_proxied
        return _CONST_PROXY[const.value.__class__]
    KeyError: <type 'numpy.ufunc'>

when linting code referencing pandas. The problem is actually with
some numpy `ufunc`, such as numpy.sin, but we don't seem to have code
using it in the test suite.