[VnV][telemac3d] Update uneven example with better choices for a few options

- TREATMENT OF NEGATIVE DEPTHS = 2 (new default value since release 9.0),
- IMPLICITATION OF VELOCITIES, ACCURACY FOR PPE, TIDAL FLATS set to their
default value,
- SCHEME FOR DIFFUSION OF VELOCITIES = 1 (with diffusion coefficients = 0)
rather than 0 to have no diffusion.
CPU time is a little bit shorter.
Mass conservation is improved (to machine precision, rather than 5 times
more of magnitude).