[hooks] build EnsureSymmetricRelations{Add,Delete} dynamically Instead of setting the __select__ attribute at registration time, which confuses the filterable_selectors cache when running different tests (with different schemas) in the same process, just make entirely new classes. Closes #8785708.

#!/usr/bin/make -f

export NO_SETUPTOOLS=1

%:
	dh $@ --with python2

override_dh_python2:
	dh_python2 -i /usr/share/cubicweb