Consider removing Lorenz 63 test example / disabling being part of default test suite

[matt-graham]

Lots of the test failures on nightly build are due to the dependency on OrdinaryDiffEq introduced by Lorenz 63 example model used in tests and this also slows test runs down a lot so might be worth either moving to the ParticleDA-UseCases repository or at least not having as part of the default test suite.