[views] Import _ from cubicweb rather that defining _ = unicode

The latter does not work with Python 3.

views.py

@@ -15,7 +15,7 @@
 # with this program. If not, see <http://www.gnu.org/licenses/>.
 """cubicweb-compound views/forms/actions/components for web ui"""
 
-from cubicweb import neg_role
+from cubicweb import _, neg_role
 from cubicweb.web import Redirect
 from cubicweb.predicates import (one_line_rset, adaptable, has_permission,
                                  match_form_params)
@@ -25,9 +25,6 @@
 from cubes.compound.entities import copy_entity
 
 
-_ = unicode
-
-
 class CloneAction(actions.CopyAction):
     """Just a copy action (copy is handled by edit controller below) named 'clone'."""
     __select__ = (actions.CopyAction.__select__ & one_line_rset() &