'Delete (the definition of) one `Column`.
col_name : str or int
The column\'s name or index'

def del_col(self, col_name):

    indx = _get_index(self.names, col_name)
    col = self.columns[indx]
    del self._arrays[indx]
    del self.dtype
    del self._recformats
    del self._dims
    del self.names
    del self.formats
    del self.columns[indx]
    col._remove_listener(self)
    self._notify('column_removed', self, indx)
    return self
