Simplify DashboardTemplate Organization relation
Simplify DashboardTemplate Organization relation

This removes the ForeignKeyConstraint in the most complex version of
https://docs.sqlalchemy.org/en/13/orm/relationship_persistence.html#rows-that-point-to-themselves-mutually-dependent-rows
which was causing us trouble.

lsst-sqre/ltd-keeper,lsst-sqre/ltd-keeper