Fix flake8 errors/warnings about import in cubicweb/_exceptions.py
We either ignore errors in case of name re-exports and drop re-exports
from old backwards compatibility. We fix the only occurrence of
NoSelectableObject being imported from cubicweb in tests and update the
import to use lgc instead.
.. _web_module:
:mod:`cubicweb.web`
===================
.. automodule:: cubicweb.web
Exceptions
----------
.. autoexception:: DirectResponse
.. autoexception:: InvalidSession
.. autoexception:: PublishException
.. autoexception:: LogOut
.. autoexception:: Redirect
.. autoexception:: StatusResponse
.. autoexception:: RequestError
.. autoexception:: NothingToEdit
.. autoexception:: ProcessFormError
.. autoexception:: NotFound
.. autoexception:: RemoteCallFailed