Remove option to pass `normal_direction_avg` for `NonConservativeJump` terms

[patrickersing]

@amrueda To prevent this problem in the future, should we just remove the option to pass the averaged normal direction to the NonConservativeJump part in calcflux_fhat!?

That's a good point. In general, I don't think that we'll ever want to pass the averaged normal direction to the NonConservativeJump part. However, we might want to pass Ja_ll and Ja_rr in the future(?) 🤔
I.e., we either pass no normal direction or we pass the two.

I suggest we just remove the normal direction argument in that routine for the time being. If we ever realize we need the two directions in the future, we can create a new PR.

Originally posted by @amrueda in trixi-framework/TrixiShallowWater.jl#131 (comment)

[patrickersing]

This change would be considered breaking as it requires a change in the call signature for nonconservative terms of type NonConservativeJump.

[ranocha]

Sounds reasonable. Would you like to make a PR?

[patrickersing]

While working on a PR for this, I noticed that the normal direction version of flux_nonconservative_powell_local_jump is also not a consistent jump term on curvilinear meshes.
When this was implemented we tested convergence on a straight-sided mesh, but on a warped mesh I observe a similar drop in the convergence order as in trixi-framework/TrixiShallowWater.jl#131.
I will see if I can find a way to rewrite flux_nonconservative_powell_local_jump to move the normal direction into the local part.

[amrueda]

Good catch, @patrickersing! Thanks!
We didn't realize back in the day!