[utils] Drop now-unused SizeConstrainedList
It's last usage in CubicWeb got removed from changeset '[views] remove
breadcrumbs usage to retrieve last visited page'
Related to #5456850.
usr/lib/python2*/*-packages/cubicweb/web
usr/lib/python2*/*-packages/cubicweb/wsgi
usr/share/cubicweb/cubes/shared/data
usr/share/cubicweb/cubes/shared/wdoc